If I’m not mistaken, the WorldAlignedBlend works by blending on the normal of the mesh, not the z position of the vertex like what it sounds like you’re wanting. The RMC will work fine with either case, but that plane doesn’t have its normals computed as there’s 600k vertices IIRC and the usual normal/tangent calculator is entirely too slow to calculate that in real-time. With something like the cubes in that scene it should work correctly.