How can I use customized collision mesh as simple collision

In the static mesh editor, I see there’s an option to use complex collision as simple and vice versa. I however used a custom collision mesh for my static mesh. By default I see that this goes on the “Custom Collision” channel, ie if I enable viewing of Complex Collision above I will see my collision and not the automatically generated complex collision. Now I want to use my complex custom collision as simple so I do Collision Complexity -> Use Complex Collision as Simple (since without that the mesh is acting as if it has no collision for simple-collision-checking; I checked). When I do that and then check to view the Simple Collision I see the automatically generated complex collision being assigned as Simple Collision and not my own custom/complex collision.

This is unacceptable as the automatically generated complex collision is too complex for my needs and I would like to use my own custom one as simple collision.

To reiterate how do I use my custom collision as simple collision? Thanks.