The color of the t shirt matters a lot when it comes to effective concealing a weapon under it. The darker the color, the better it will 'hide' any profile that the weapon might produce. I carry a G26 in a Crossbreed Super Tuck Deluxe, and only wear dark polo's and t shirts with it. It's a simple thing that goes a long way. Wear a dark shirt and have someone look at you and tell you if you are profiling in different positions.
"If a law is unjust, a man is not only right to disobey it, he is obligated to do so." - Thomas Jefferson