You shouldn’t have to do any .ini renaming for the original Ethan Carter, the game has a dedicated profile that will work a lot better than using the generic UE3 profile. IIRC it even has DirectVR memory scan head tracking, using mouse based tracking is quite laggy in this game.
Not sure about the Redux version, never tried it. Just use the original, highly doubtful that you will notice any difference in regard to texture resolution anyway in a VR headset unless you stand directly in front of a wall/tree/whatever.