diff --git a/tests/AcDream.Core.Tests/Streaming/StreamingRegionTwoTierTests.cs b/tests/AcDream.Core.Tests/Streaming/StreamingRegionTwoTierTests.cs
index ccf8f13..65df093 100644
--- a/tests/AcDream.Core.Tests/Streaming/StreamingRegionTwoTierTests.cs
+++ b/tests/AcDream.Core.Tests/Streaming/StreamingRegionTwoTierTests.cs
@@ -14,5 +14,10 @@ public class StreamingRegionTwoTierTests
         Assert.Equal(12, region.FarRadius);
         Assert.Equal(100, region.CenterX);
         Assert.Equal(100, region.CenterY);
+        // Radius (used by existing single-radius hysteresis math) must alias to
+        // FarRadius — the outer ring drives "everything currently loaded" bookkeeping.
+        // If a future change mistakenly aliases Radius to NearRadius, hysteresis
+        // becomes (NearRadius+2) for the far-tier unload, which is wrong.
+        Assert.Equal(region.FarRadius, region.Radius);
     }
 }