For my subcompact Glock, there was no question in my mind that the better arrangement was the rear backup iron sight mounted in the standard dovetail and behind the RMR. There were a few reasons upon which I based my decision:
- Moving the rear iron sight in front of the RMR sacrifices a large percentage of the sight radius distance on a subcompact pistol that is already short.
- The tall suppressor sights are intended to be functional backup sights in case of RMR failure. BUIS in the standard locations leverage the thousands of repetitions and long hours of training that one has practiced with iron sights and at the maximum possible sight radius for the pistol.
- Tritium lamps on the front and rear suppressor sights are a definite advantage to orient the pistol quickly in low light and get the red dot on target. I've tried it both with and without tritium lamps in timed exercises. Any part of the RMR that momentarily obstructs your view of the rear tritium lamps as the pistol is drawn and presented is a disadvantage in my opinion.
- If the rear sight dovetail remains stock, the pistol can be returned to near stock function and appearance by removing the RMR and installing in its place a slide cover plate custom milled for the slide cutout.
Here is a link to opposing arguments from GT member JakAttak
for placing the rear iron sight in front of the RMR.
I can see merit to some of the points he made, but I'm entirely comfortable with the decision I made and will repeat the same configuration on my next pistol RMR installation. Don't bother checking WarriorTalk.com for opinions. They all run the rear iron sight behind the RMR over there.