With a good belt, kept relatively snug, I'd imagine any "sag" would be negligible. However, I don't have first hand experience to guarantee it. If you do some reading on the pistol centric forums, you'll see users who run them behind the belt with good results. You'll even have people who use them without a belt. I looked into them about a year ago, and they seemed promising. I'll see if I can dig up some threads/videos that specifically discuss being used behind, or without, a belt.