When you have a shirt draped over a pistol, and the shirt gets pulled up(bending over or reaching up to a shelf), a real grippy pistol will tend to keep the shirt up so the pistol could be seen below the shirt or the bulge of fabric would be more noticeable. Or, if you twist your upper body to one side, a grippy pistol will grab the shirt fabric and the shirt will get stretched tightly over the pistol. Looking at it from a different perspective, a real soft knit shirt shows more than a shirt made from something more like a thin canvas.