This isn’t the answer you’re looking for, but my solution has been to lift my rift to my forehead, so that it still detects my forehead and thinks I’m inside.
This isn’t perfectly ideal so I’ll be watching if someone has an actual answer for an option that keeps it enabled. That seems like a thing that should exist
I’m surprised there isn’t a “Keep HMD Display On” function, or a way to access/disable the proximity sensor. Or maybe a function/tag for the mirror window, to keep the game running even if proximity sensor turns off the HMD. UE4 also needs WAY more control over the mirror/preview window.
I really wish I could turn the preview window into an in-game security camera perspective, to show players outside VR a non-first-person view from the game.