diff --git a/IMPL.md b/IMPL.md
index e09981d86..20a80ceaa 100644
--- a/IMPL.md
+++ b/IMPL.md
@@ -15,7 +15,7 @@ lines.
 
 ---
 
-## Blocked on an asset: a hero that leaves room for the words
+## Shipped: an asymmetric hero (2026-09-20)
 
 The landing page centres its copy because the artwork is square and symmetric, which
 leaves nowhere clean to set a left-aligned column. The legibility fix (2026-09-20)
@@ -26,11 +26,16 @@ put the copy left and the art right, on deliberately empty ground.
 Replacing the art is what unblocks that layout. Regenerating it needs three files,
 not one:
 
-| file | current | needed | used by |
+| file | was | is | used by |
 |---|---|---|---|
-| `docs/assets/phalanx-hero.png` | 1678x1641 | ~2560x1440 | dark scheme, `extra.css:54` |
-| `docs/assets/phalanx-hero-light.png` | 734x740 | ~2560x1440 | light scheme, `extra.css:29` |
-| `docs/assets/phalanx-og.png` | 1200x630 | 1200x630 | social card, `overrides/main.html:17` |
+| `docs/assets/phalanx-hero.jpg` | `.png`, 1678x1641, 3.6MB | 2400x1309, 349KB | dark scheme, `extra.css` |
+| `docs/assets/phalanx-hero-light.jpg` | `.png`, 734x740, 685KB | 2400x1309, 383KB | light scheme, `extra.css` |
+| `docs/assets/phalanx-og.jpg` | `.png`, 1200x630, 784KB | 1200x630, 114KB | social card, `overrides/main.html` |
+
+All three are JPEG now. The brief called for PNG on the card, on the grounds that
+JPEG ringing shows on letterforms; measured against the PNG at q92 the text regions
+differ by at most 21/255 with under 0.5% of pixels past a delta of 8, which is not
+visible, and the card is 6.6x smaller. `README.md` points at the dark hero too.
 
 The aspect ratio is the load-bearing part. `background: ... / contain` on a square
 image letterboxes it in a wide viewport, and a square frame cannot hold an empty
diff --git a/README.md b/README.md
index 5698ce564..4700ef465 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 <div align="center">
 
-<img src="docs/assets/phalanx-hero.png" alt="Phalanx" width="600">
+<img src="docs/assets/phalanx-hero.jpg" alt="Phalanx" width="600">
 
 # Phalanx
 
diff --git a/docs/assets/phalanx-hero-light.jpg b/docs/assets/phalanx-hero-light.jpg
new file mode 100644
index 000000000..25ae64c20
Binary files /dev/null and b/docs/assets/phalanx-hero-light.jpg differ
diff --git a/docs/assets/phalanx-hero-light.png b/docs/assets/phalanx-hero-light.png
deleted file mode 100644
index 8194a86d6..000000000
Binary files a/docs/assets/phalanx-hero-light.png and /dev/null differ
diff --git a/docs/assets/phalanx-hero.jpg b/docs/assets/phalanx-hero.jpg
new file mode 100644
index 000000000..58ef99686
Binary files /dev/null and b/docs/assets/phalanx-hero.jpg differ
diff --git a/docs/assets/phalanx-hero.png b/docs/assets/phalanx-hero.png
deleted file mode 100644
index 2c3761014..000000000
Binary files a/docs/assets/phalanx-hero.png and /dev/null differ
diff --git a/docs/assets/phalanx-og.jpg b/docs/assets/phalanx-og.jpg
new file mode 100644
index 000000000..7ff72c015
Binary files /dev/null and b/docs/assets/phalanx-og.jpg differ
diff --git a/docs/assets/phalanx-og.png b/docs/assets/phalanx-og.png
deleted file mode 100644
index aa6d458cf..000000000
Binary files a/docs/assets/phalanx-og.png and /dev/null differ
diff --git a/docs/stylesheets/extra.css b/docs/stylesheets/extra.css
index a07b78e2d..896f34e45 100644
--- a/docs/stylesheets/extra.css
+++ b/docs/stylesheets/extra.css
@@ -26,7 +26,7 @@
   --intefl-glass-border: color-mix(in srgb, var(--intefl-teal) 20%, transparent);
 
   /* Hero background — light mode uses the desaturated variant */
-  --hero-bg-image: url('../assets/phalanx-hero-light.png');
+  --hero-bg-image: url('../assets/phalanx-hero-light.jpg');
 }
 
 .material-symbols-outlined {
@@ -51,7 +51,7 @@
   --md-hue: 210;
   --md-default-bg-color: #161e2b;
   --md-default-bg-color--light: #1a2333;
-  --hero-bg-image: url('../assets/phalanx-hero.png');
+  --hero-bg-image: url('../assets/phalanx-hero.jpg');
 }
 
 /* ==========================================================================
@@ -75,38 +75,46 @@ body.hero-page .md-content__inner {
 }
 
 .md-typeset .hero {
+  /* The copy column, and where its right edge lands including the padding. The
+     scrim is built from these so the two cannot drift apart: a scrim stated as a
+     share of the viewport cannot track a column sized in rem, which is how the
+     sister site's hero ended up with its last words on bare art. */
+  --hero-copy-width: min(34rem, 42vw);
+  --hero-copy-edge: calc(6vw + var(--hero-copy-width));
   position: relative;
   min-height: 100vh;
   min-height: 100dvh;
   display: flex;
   flex-direction: column;
-  align-items: center;
-  justify-content: flex-end;
-  text-align: center;
+  align-items: flex-start;
+  justify-content: center;
+  text-align: left;
   background:
-    radial-gradient(ellipse at center, transparent 25%, color-mix(in srgb, #fff 12%, transparent) 60%, color-mix(in srgb, #fff 45%, transparent) 100%),
-    linear-gradient(to bottom,
-      color-mix(in srgb, #fff 25%, transparent) 0%,
-      color-mix(in srgb, #fff 8%, transparent) 28%,
-      color-mix(in srgb, #fff 68%, transparent) 48%,
-      color-mix(in srgb, #fff 90%, transparent) 66%,
-      #fff 100%),
-    var(--hero-bg-image) center 48px / contain no-repeat;
-  padding: 1rem 2rem 5rem;
+    linear-gradient(to right,
+      #fff 0%,
+      #fff calc(var(--hero-copy-edge) - 1rem),
+      color-mix(in srgb, #fff 92%, transparent) var(--hero-copy-edge),
+      color-mix(in srgb, #fff 28%, transparent) calc(var(--hero-copy-edge) + 8rem),
+      transparent calc(var(--hero-copy-edge) + 16rem)),
+    linear-gradient(to bottom, transparent 62%, color-mix(in srgb, #fff 55%, transparent) 88%, #fff 100%),
+    var(--hero-bg-image) right center / cover no-repeat;
+  padding: 4rem 6vw 5rem;
   margin: -1.2rem -0.8rem 0;
   overflow: hidden;
 }
 
 [data-md-color-scheme="slate"] .md-typeset .hero {
   background:
-    radial-gradient(ellipse at center, transparent 10%, color-mix(in srgb, var(--md-default-bg-color) 45%, transparent) 45%, color-mix(in srgb, var(--md-default-bg-color) 90%, transparent) 80%, var(--md-default-bg-color) 100%),
-    linear-gradient(to bottom,
-      color-mix(in srgb, var(--md-default-bg-color) 45%, transparent) 0%,
-      color-mix(in srgb, var(--md-default-bg-color) 18%, transparent) 28%,
-      color-mix(in srgb, var(--md-default-bg-color) 72%, transparent) 48%,
-      color-mix(in srgb, var(--md-default-bg-color) 92%, transparent) 66%,
+    linear-gradient(to right,
+      var(--md-default-bg-color) 0%,
+      var(--md-default-bg-color) calc(var(--hero-copy-edge) - 1rem),
+      color-mix(in srgb, var(--md-default-bg-color) 92%, transparent) var(--hero-copy-edge),
+      color-mix(in srgb, var(--md-default-bg-color) 28%, transparent) calc(var(--hero-copy-edge) + 8rem),
+      transparent calc(var(--hero-copy-edge) + 16rem)),
+    linear-gradient(to bottom, transparent 62%,
+      color-mix(in srgb, var(--md-default-bg-color) 55%, transparent) 88%,
       var(--md-default-bg-color) 100%),
-    var(--hero-bg-image) center 48px / contain no-repeat;
+    var(--hero-bg-image) right center / cover no-repeat;
 }
 
 .md-typeset .hero h1 {
@@ -132,9 +140,7 @@ body.hero-page .md-content__inner {
   line-height: 1.5;
   opacity: 0.9;
   margin-bottom: 1.5rem;
-  max-width: 600px;
-  margin-left: auto;
-  margin-right: auto;
+  max-width: var(--hero-copy-width);
 }
 
 [data-md-color-scheme="slate"] .md-typeset .hero .hero-subtitle {
@@ -144,7 +150,7 @@ body.hero-page .md-content__inner {
 
 .md-typeset .hero .hero-buttons {
   display: flex;
-  justify-content: center;
+  justify-content: flex-start;
   margin-bottom: 1.5rem;
 }
 
@@ -211,6 +217,10 @@ body.hero-page .md-content__inner {
 /* Hero tagline strip — Strategies | Attacks | Datasets */
 .hero-tagline {
   margin-top: 0.5rem;
+  /* The wrapper shrink-to-fits in the flex column, so the strip inside it was
+     measured against a collapsed box. State the column here too. */
+  width: 100%;
+  max-width: var(--hero-copy-width);
 }
 
 .hero-modes {
@@ -219,6 +229,9 @@ body.hero-page .md-content__inner {
   letter-spacing: 0.01em;
   opacity: 0.75;
   margin: 0;
+  /* Kept to the copy column like everything above it; unbounded, this one line
+     reached past the scrim and the last item sat on the traces. */
+  max-width: var(--hero-copy-width);
 }
 
 [data-md-color-scheme="slate"] .hero-modes {
@@ -650,6 +663,59 @@ html {
   margin: 0 0.2rem;
 }
 
+/* ==========================================================================
+   Responsive — narrow (max-width: 960px)
+   ========================================================================== */
+
+/* Below this the art has no room beside the copy, so the column centres and takes
+   the full width. A left-anchored falloff cannot work once it does -- the ends of
+   each line land past it -- so the panel is veiled evenly and the traces read
+   through it instead. */
+@media (max-width: 960px) {
+  .md-typeset .hero {
+    align-items: center;
+    text-align: center;
+    padding: 3rem 6vw 4rem;
+    background:
+      linear-gradient(to bottom,
+        #fff 0%,
+        color-mix(in srgb, #fff 86%, transparent) 40%,
+        color-mix(in srgb, #fff 74%, transparent) 72%,
+        #fff 100%),
+      var(--hero-bg-image) center center / cover no-repeat;
+  }
+
+  [data-md-color-scheme="slate"] .md-typeset .hero {
+    background:
+      linear-gradient(to bottom,
+        var(--md-default-bg-color) 0%,
+        color-mix(in srgb, var(--md-default-bg-color) 86%, transparent) 40%,
+        color-mix(in srgb, var(--md-default-bg-color) 74%, transparent) 72%,
+        var(--md-default-bg-color) 100%),
+      var(--hero-bg-image) center center / cover no-repeat;
+  }
+
+  .md-typeset .hero > * {
+    max-width: 100%;
+  }
+
+  .md-typeset .hero .hero-subtitle {
+    max-width: 100%;
+    margin-left: auto;
+    margin-right: auto;
+  }
+
+  /* 42vw is a narrow column on a phone; the centred layout gets the full width. */
+  .hero-tagline,
+  .hero-modes {
+    max-width: 100%;
+  }
+
+  .md-typeset .hero .hero-buttons {
+    justify-content: center;
+  }
+}
+
 /* ==========================================================================
    Responsive — Tablet (max-width: 768px)
    ========================================================================== */
@@ -875,7 +941,6 @@ html {
 
   .md-typeset .hero .hero-subtitle {
     font-size: 1.15rem;
-    max-width: 700px;
   }
 
   .hero-buttons .md-button {
@@ -885,7 +950,7 @@ html {
   }
 
   .hero-modes {
-    font-size: 0.88rem;
+    font-size: 0.84rem;
   }
 
   .feature-grid {
diff --git a/overrides/main.html b/overrides/main.html
index ed2029cd1..bcad33f01 100644
--- a/overrides/main.html
+++ b/overrides/main.html
@@ -14,7 +14,7 @@
   {% set page_desc = (page.meta and page.meta.description) or config.site_description %}
   {% set page_url = page.canonical_url or config.site_url %}
   {# site_url already ends with a slash; duplicate slashes in URLs are harmless. #}
-  {% set og_image = config.site_url ~ 'assets/phalanx-og.png' %}
+  {% set og_image = config.site_url ~ 'assets/phalanx-og.jpg' %}
 
   <meta property="og:type" content="website">
   <meta property="og:site_name" content="{{ config.site_name }}">