Often times, I carry a full size XD40 in an MTAC IWB at 3:30 while in church when I'm not carrying my 642 in the pocket. As an Episcopalian, I'm constantly doing the Holy Calesthenics (kneeling, standing, etc.). We're pretty casual, so it's usually just with an untucked camp shirt or something similar. I've even tucked the shirt in since it's a tuckable holster. No worries. People right behind me never noticed. As others have said, I just try to not bend at the waist. I'm thinking I'm the only one that looks for printing, simply because I'm aware--and I know that I'm not the only sheepdog in church every morning.
I am fortunate that my G26 conceals very well. Except with a few very fitted T-shirts I have no issues. You MUST have a good gun belt and holster.
If your back and shoulders are wider than your waist you pretty much can conceal anything (do a lot of pushups).