Fighting Through Snags
Categorically make sure the students fight through snags. A snag is where the clothing gets caught up with the pistol and causes issues in the draw process. There are no do-overs in a critical incident; to establish a psychological foundation have them fight through any kind of snag. Remember the SIRT pistols are inert but they should respect the muzzle, keep their finger out of the trigger as they get the SIRT away from the clothing, establish the grip and start the presentation grip establishment process.
Snags will eventually happen. As they grab the pistol, clothing is loose and free flowing and will interpose between the hand and the grip area. Sometimes this clears out on its own but other times the whole muzzle can get entangled within the garment. Of course this is good to do and vet out in training particularly under time pressure because they need to get an appreciation of how to clear away that garment safely while respecting the trigger and making sure nothing gets in the trigger guard. While fighting through the snag the students also must respect the orientation of the muzzle so they do not point the muzzle pointing at anything they are not willing to destroy.
Further, if you have time you can have people change their garment into just a front open garment so they work the same process with appendix and 4:00 so they know they can pull the garment over from appendix say with their right hand as they establish their grip. But moreover this is a more common way to carry at 4:00 where both hand sweep the garment over behind them while holding it with the left hand (with right-handed shooter) they establish the grip with the strong hand, again thumb over the sights and they withdraw the pistol and again begin the grip establishment, full extension process.