I am not sure why folks, who also carry three o'clock for work, gun games, or otherwise, do much live fire practice from appendix. The difference between AIWB and three o'clock, is the draw, and dry fire is a very efficient way to practice drawing.
A few years ago, I made a decision to live fire from OWB and dry fire from appendix. A week or two ago, I forgot my OWB holster at home, and did my live fire session with a G19 out of my AIWB holster. First real live fire appendix session in a year or more, and my live fire confirmed that dry fire worked as I expected.
The law of large numbers says, regardless of platform and technique, the more people doing something such as AIWB, the greater the likelihood of an ND. And with AIWB, regardless of the odds, the stakes are enormous. I think there are a number of reasons folks live fire from AIWB -- some good and most bad. A good reason being that is the ONLY way they carry, and don't want to learn a different draw. Some bad reasons are: it is perceived as cool, they never considered an alternative like dry fire AIWB draw practice, and the vanity of wanting a .1 or .2 faster draw from concealment over concealed OWB when doing PF oriented drills.
I recognize each person gets to decide, but I would like folks to consider there are alternatives, given the stakes.