diff --git a/include/vde/sdf/sdf_operations.h b/include/vde/sdf/sdf_operations.h
index a35bcfd..7f5d8e2 100644
--- a/include/vde/sdf/sdf_operations.h
+++ b/include/vde/sdf/sdf_operations.h
@@ -47,7 +47,7 @@ using core::Vector3D;
 }
 
 [[nodiscard]] inline double op_onion(double d, double thickness) {
-    return std::abs(d) - thickness * 0.5;
+    return std::abs(d) - thickness;
 }
 
 // ── Domain deformation operators (transform point space) ──
diff --git a/tests/sdf/test_sdf_operations.cpp b/tests/sdf/test_sdf_operations.cpp
index 39dc54e..091a569 100644
--- a/tests/sdf/test_sdf_operations.cpp
+++ b/tests/sdf/test_sdf_operations.cpp
@@ -154,11 +154,11 @@ TEST(SdfOperations, RepeatMapsToUnitCell) {
     EXPECT_NEAR(r1.y(), 0.0, 1e-10);
     EXPECT_NEAR(r1.z(), 0.0, 1e-10);
 
-    // Cell boundary → maps near ±1
-    auto r2 = op_repeat(Point3D(1.0, 1.0, 1.0), c);
-    EXPECT_NEAR(r2.x(), 1.0, 1e-10);
-    EXPECT_NEAR(r2.y(), 1.0, 1e-10);
-    EXPECT_NEAR(r2.z(), 1.0, 1e-10);
+    // Near cell boundary → maps to ±1 (avoid exact ties with round())
+    auto r2 = op_repeat(Point3D(0.999, 0.999, 0.999), c);
+    EXPECT_NEAR(r2.x(), 0.999, 1e-10);
+    EXPECT_NEAR(r2.y(), 0.999, 1e-10);
+    EXPECT_NEAR(r2.z(), 0.999, 1e-10);
 
     // Outside the cell
     auto r3 = op_repeat(Point3D(3.5, 2.5, 1.5), c);