I haven't tried carrying a full-sized pistol IWB, but I think it would be hard for me to do because I'm short (5'6") and short-waisted to boot. I carry an FNS-9 OWB and it works O.K. (and the gun suits me better than any other 9mm with a double-stack magazine that I've tried). When I carry either my Ruger LCR or my S&W Shield IWB in either the appendix or cross-draw position, they gouge me in the thigh when I'm sitting. So, I can't believe that I could carry a full-sized pistol IWB in one of those positions. And, due to shoulder problems, the 3:30 position is just about out of the question.
Crash