One way I check to make sure my shirt is down over the butt of my gun is to either reach for my wallet and brush down against my waist, or hike my pants up a bit, which, being a young guy with slightly-droopy pants, is completely normal looking
Sometimes I do carry a smaller Bersa .380 and I certainly notice a difference in how I feel. The smaller frame really helps conceal it in my waistband and even if it was to poke out of my shirt, it's probably not too noticeable. I wear it low inside my waistband in a crossbreed holster. My Beretta 9mm I usually wear higher in a crossbreed as well.