Ok, I think I found a solution
physx_convexdecomp_api = PhysxSchema.PhysxConvexDecompositionCollisionAPI.Apply(prim)
physx_convexdecomp_api.GetShrinkWrapAttr().Set(True)
It is hard to know about these APIs to the lack of typing information in the code.
See other forum issue: How to get python typing information for the pxr PhysxSchema? - Omniverse / Isaac Sim - NVIDIA Developer Forums
Docs: PhysxSchemaPhysxConvexDecompositionCollisionAPI Class Reference (nvidia.com)
The tray collider mesh is now approximating well and the cube appears to rest on it as expected.
