diff --git a/presentation/deck/index.html b/presentation/deck/index.html
index 8a46b0d5..5a687baf 100644
--- a/presentation/deck/index.html
+++ b/presentation/deck/index.html
@@ -561,9 +561,10 @@
     const cx = (marts.left + marts.width / 2 - rwrap.left) / s;
     const railLeft = (rail.left - rwrap.left) / s;
     const railTop = (rail.top - rwrap.top) / s;
+    const mBottom = (marts.bottom - rwrap.top) / s;
     drop.style.left = (cx - 1) + 'px';
-    drop.style.top = ((marts.top - rwrap.top) / s) + 'px';
-    drop.style.height = Math.max(0, railTop - (marts.top - rwrap.top) / s) + 'px';
+    drop.style.top = mBottom + 'px';
+    drop.style.height = Math.max(0, railTop - mBottom) + 'px';
     elbow.style.left = railLeft + 'px';
     elbow.style.width = Math.max(0, cx - railLeft) + 'px';
     elbow.style.top = (railTop - 1) + 'px';