I had a super-tuck from crossbreed, and I could carry a full-sized cz-75 at work with just a t-shirt but I had to have the holster on JUST RIGHT, and I had to have my belt TIGHT, however it was extremely uncomfortable and all that tension with a heavier gun and tight belt broke the snaps on it, started to wear out the holes in the leather and when those holes got rough it would squeak... so I trashed it
that being said, I don't usually carry a full sized gun anymore because being so super-stiff with my posture really doesn't make anything easier (except wearing out my knees and back). IF I do carry a full size, I use a regular belt slide holster but between my right buttcheek and hip I skip a belt loop so the belt isn't looped where the gun should go for strong-side carry.... which allows me to tuck the whole holster into my pants like an iwb but with my jeans pulled down just enough on the edge of the holster that I can't snag my pants easily at all, and that works great but you CANNOT really trust a shirt to cover that one up, missing a loop and having your pants slightly pulled down will look really odd unless you have a very long shirt to cover that when you bend over. If someone stares hard enough they might figure out when you missed a belt-loop.
method two I use when I don't feel like wearing a bellyband at the gym, or if I'm going to REALLY be moving around and don't trust a belt rig to not show, and that method is to use an extremely small, tight-fitting pocket holster and I wear it over my crotch-- just wait, it gets better,-- I wear boxer briefs, over those I wear regular briefs, and between the two is where the pocket holster goes... believe me if you try this with a snub no one will EVER have any idea, of course you need to tighten your drawstring with shorts, belt with jeans/pants, and make sure you adjust your package well before you go out or people are going to think you have herpes because you dig at yourself so much... don't use any weapons with sharp/unradiused sights
option three is to use a regular belt and holster as a bellyband (works much better than the real thing, assuming you can still breathe) and that works for full sized guns as long as they have a flat profile (1911 GI will do nicely) but it'll settle between your ribs so you better use a very stiff and wide belt (be sure that the belt-buckle doesn't show through your shirt, and if you sweat alot it won't work, and you'll get pit juice in your slide)