Merging assets converts UBX to UCX

Hello!
So, I have a problem that I think is either user error, or maybe an easy fix for epic to make:
Whenever I have a static mesh that has UBX/Box collisions, generated in engine, or made in 3D software (I’ve tested both) after merging, the collisions are then converted to UCX/Convex element. When making content for mobile or VR, there are performance gains to use UBX boxes compared to UCX boxes. Is there a way to merge multiple meshes and retain their original collision types?

Also, when exporting these meshes from engine to FBX for editing, the collisions are grouped into one mesh that make it tough to separate and re-constitute collisions correctly.

Has anyone else come across these issues? Is there a reasonable fix or work around? I have tried many different settings when merging and exporting and nothing seems to make a difference.