diff --git a/public/js/webgl-book-shape-lab.js b/public/js/webgl-book-shape-lab.js
index 2b3d9f7..73eb656 100644
--- a/public/js/webgl-book-shape-lab.js
+++ b/public/js/webgl-book-shape-lab.js
@@ -296,20 +296,7 @@ function addCoverAssembly(pageWidth, depth, thickness, spineWidth, coverOuterX)
 }
 
 function createCoverAssemblyGeometry(pageWidth, depth, thickness, spineWidth, coverOuterX) {
-    const spineHalf = spineArcHalf(spineWidth);
-    const hingeX = spineHalf + hingeInset();
-    const outerX = coverOuterX ?? spineHalf + pageWidth + COVER_OVERHANG;
-    const outerTopY = BOOK_PROFILE.tableY + thickness;
-    const connectionTopY = BOOK_PROFILE.raisedHingeY;
-    const spineTopY = BOOK_PROFILE.tableY + thickness;
-    const section = [
-        { x: -outerX, y: outerTopY },
-        { x: -hingeX, y: connectionTopY },
-        { x: -spineHalf, y: spineTopY },
-        { x: spineHalf, y: spineTopY },
-        { x: hingeX, y: connectionTopY },
-        { x: outerX, y: outerTopY }
-    ];
+    const section = coverProfilePoints(spineWidth, coverOuterX ?? spineArcHalf(spineWidth) + pageWidth + COVER_OVERHANG);
     const positions = [];
     const uvs = [];
     const indices = [];
@@ -409,6 +396,25 @@ function hingeInset() {
     return Math.max(0.001, BOOK_PROFILE.raisedHingeY - BOOK_PROFILE.coverThickness);
 }
 
+function coverProfilePoints(spineWidth, coverOuterX) {
+    return coverProfilePointsFromFrame(spineArcHalf(spineWidth), coverOuterX);
+}
+
+function coverProfilePointsFromFrame(spineHalf, coverOuterX) {
+    const hingeX = spineHalf + hingeInset();
+    const outerTopY = BOOK_PROFILE.tableY + BOOK_PROFILE.coverThickness;
+    const connectionTopY = BOOK_PROFILE.raisedHingeY;
+    const spineTopY = BOOK_PROFILE.tableY + BOOK_PROFILE.coverThickness;
+    return [
+        { x: -coverOuterX, y: outerTopY },
+        { x: -hingeX, y: connectionTopY },
+        { x: -spineHalf, y: spineTopY },
+        { x: spineHalf, y: spineTopY },
+        { x: hingeX, y: connectionTopY },
+        { x: coverOuterX, y: outerTopY }
+    ];
+}
+
 function calculateSpineWidth(bundleCount) {
     const minimumWidth = 0.16;
     if (bundleCount <= 1) return minimumWidth;
@@ -894,16 +900,19 @@ function upwardNormalAt(points, index) {
 
 function coverTopYAtX(x) {
     const ax = Math.abs(x);
-    const spineHalf = currentSpineHalf();
-    const hingeX = spineHalf + hingeInset();
-    const outerX = activeCoverOuterX;
-    if (ax <= spineHalf) return BOOK_PROFILE.coverThickness;
-    if (ax <= hingeX) {
-        const t = (ax - spineHalf) / (hingeX - spineHalf);
-        return THREE.MathUtils.lerp(BOOK_PROFILE.coverThickness, BOOK_PROFILE.raisedHingeY, t);
+    const profile = coverProfilePointsFromFrame(currentSpineHalf(), activeCoverOuterX)
+        .filter((point) => point.x >= 0)
+        .sort((a, b) => a.x - b.x);
+    if (ax <= profile[0].x) return profile[0].y;
+    for (let index = 0; index < profile.length - 1; index += 1) {
+        const from = profile[index];
+        const to = profile[index + 1];
+        if (ax <= to.x) {
+            const t = (ax - from.x) / (to.x - from.x || 1);
+            return THREE.MathUtils.lerp(from.y, to.y, t);
+        }
     }
-    const t = THREE.MathUtils.clamp((ax - hingeX) / (outerX - hingeX), 0, 1);
-    return THREE.MathUtils.lerp(BOOK_PROFILE.raisedHingeY, BOOK_PROFILE.coverThickness, t);
+    return profile[profile.length - 1].y;
 }
 
 function currentSpineHalf() {