Sphere Collider overlap not triggering with Object Channel?

I am expecting an overlap event to fire but it is not.
I have an actor with a static mesh with physics enabled and a child sphere component. The mesh is set to Object Type = Metal and the sphere component is set with Object responses > Metal = Overlap.
I would expect that if I place two of these actors in my level and push one mesh into the sphere of the other, there would be a BeginOverlap event but there is not. Am I misunderstanding something here?

The event does fire if I set the sphere to Object responses > WorldStatic = Overlap but why is the cube mesh responding as if WorldStatic when I have set it to my custom object channel Metal?