I carried at the 4 o'clock position for probably 20 years. In Feb 2007, I took Extreme Close-Range Gunfighting from Gabe Suarez.
During this class, he recommended we at least try Appendix, specifically Appendix inside the waist band (AIWB). Initially, I parcticed around the house with unloaded weapons (Colt Defender, Glock 30). After a few weeks, I got used to it, and it has been my preferred carry mode for over a year now. I have changed to a Glock 19 or 26 for my primary pistols now.
Body type does play a part in this carry method, I'm 5'11 and weigh 230. Although overweight, I don't find this method uncomfortable. It is extremely fast, with less body movement to bring the pistol into action. And it allows easy presentation while moving off the line of fire (i.e: Getting Off The “X”).
I also carry my cellphone case on the outside of the belt with the gun holstered AIWB behind it. If someone does bump into me there and questions what they hit, I can show them the phone. It has worked twice so far.