diff --git a/OpenNest.Engine.Tests/Fill/SortStripsTests.cs b/OpenNest.Engine.Tests/Fill/SortStripsTests.cs
new file mode 100644
index 0000000..40bce6e
--- /dev/null
+++ b/OpenNest.Engine.Tests/Fill/SortStripsTests.cs
@@ -0,0 +1,46 @@
+using OpenNest.Engine.Fill;
+using OpenNest.Geometry;
+
+namespace OpenNest.Engine.Tests.Fill;
+
+public class SortStripsTests
+{
+    private static Part MakeRectPart(double x, double y, double w, double h)
+    {
+        var pgm = new OpenNest.CNC.Program();
+        pgm.Codes.Add(new OpenNest.CNC.RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new OpenNest.CNC.LinearMove(new Vector(w, 0)));
+        pgm.Codes.Add(new OpenNest.CNC.LinearMove(new Vector(w, h)));
+        pgm.Codes.Add(new OpenNest.CNC.LinearMove(new Vector(0, h)));
+        pgm.Codes.Add(new OpenNest.CNC.LinearMove(new Vector(0, 0)));
+        var drawing = new Drawing("rect", pgm);
+        return new Part(drawing, new Vector(x, y));
+    }
+
+    [Fact]
+    public void SortColumnsByHeight_NonUniformGaps_DoesNotExceedOriginalSpan()
+    {
+        // Three columns with non-uniform gaps between them (5, then 1) and heights
+        // ordered so the sort-by-height pass must reorder them (tallest first, then
+        // shortest, then medium). The tallest column's original position leaves a
+        // 5-unit gap to its neighbor; that single sampled gap must not get replayed
+        // as the spacing for the whole staircase once it's no longer the leading pair.
+        var tall = MakeRectPart(0, 0, 10, 30);    // Left 0-10,  gap of 5 to next
+        var shortCol = MakeRectPart(15, 0, 5, 5); // Left 15-20, gap of 1 to next
+        var medium = MakeRectPart(21, 0, 20, 15); // Left 21-41
+
+        var originalRight = new[] { tall, shortCol, medium }.Max(p => p.BoundingBox.Right);
+        var originalLeft = new[] { tall, shortCol, medium }.Min(p => p.BoundingBox.Left);
+        var originalSpan = originalRight - originalLeft;
+
+        var parts = new List<Part> { tall, shortCol, medium };
+        IterativeShrinkFiller.SortColumnsByHeight(parts, spacing: 1.0);
+
+        var newRight = parts.Max(p => p.BoundingBox.Right);
+        var newLeft = parts.Min(p => p.BoundingBox.Left);
+        var newSpan = newRight - newLeft;
+
+        Assert.True(newSpan <= originalSpan + 1e-9,
+            $"Resequenced columns must not exceed the original footprint: original span {originalSpan}, new span {newSpan}");
+    }
+}
diff --git a/OpenNest.Engine/Fill/IterativeShrinkFiller.cs b/OpenNest.Engine/Fill/IterativeShrinkFiller.cs
index 790148c..2669804 100644
--- a/OpenNest.Engine/Fill/IterativeShrinkFiller.cs
+++ b/OpenNest.Engine/Fill/IterativeShrinkFiller.cs
@@ -219,8 +219,10 @@ namespace OpenNest.Engine.Fill
             if (strips.Count <= 1)
                 return;
 
-            var gap = stripMin(strips[1]) - stripMax(strips[0]);
-
+            // Use the required clearance as the inter-strip gap, not a gap sampled from one
+            // original pair: actual placement gaps vary for irregular/mixed-size geometry, and
+            // replaying a larger sampled gap across every reordered pair can push the trailing
+            // strip past the original (already plate-fitted) footprint.
             strips.Sort((a, b) => sortMetric(a).CompareTo(sortMetric(b)));
 
             var pos = primaryEdge(parts[0].BoundingBox);
@@ -236,7 +238,7 @@ namespace OpenNest.Engine.Fill
                         part.Offset(offset);
                 }
 
-                pos = stripMax(s) + gap;
+                pos = stripMax(s) + spacing;
             }
 
             parts.Clear();
diff --git a/OpenNest.Engine/OpenNest.Engine.csproj b/OpenNest.Engine/OpenNest.Engine.csproj
index d873f47..f9ac952 100644
--- a/OpenNest.Engine/OpenNest.Engine.csproj
+++ b/OpenNest.Engine/OpenNest.Engine.csproj
@@ -6,6 +6,7 @@
   </PropertyGroup>
   <ItemGroup>
     <InternalsVisibleTo Include="OpenNest.Tests" />
+    <InternalsVisibleTo Include="OpenNest.Engine.Tests" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\OpenNest.Core\OpenNest.Core.csproj" />