Okay I have made up my mind after a short test. I compared the beam of the XR-E McR-17-XR with my current L2P (standard reflector and LuxIII). Apparently my current L2P has a sidespill that's around 60% larger (in diameter) than the McR-17-XR. Assuming turning down the end (end = side where the light comes out) of the McR-17-XR will lead to more sidespill (as in "wider beam") (and less throw, but hell, right now at 350 mA it already outthrows a 700 mA UX1J), I consider to do this to have around the same sidespill as with my current L2P (it's perfect for my needs).
And in case 4 mm is too much to get of the end of the reflector, I can get something off the LE since I have around 1 to 2 mm left in there.