In this thread, a number of posters indicated that they found the ride height of some popular AIWB holsters to be too low. I've been a fan of AIWB holsters that ride just high enough to get a full grip on the gun since I got an appendix Looper several years ago. When I first got the Looper I also felt that it rode too low, and I repeatedly smashed my knuckles into my belt when doing full speed draws. Then, I made a very small change to my AIWB draw technique and the knuckle smashing went away. (I likely got this technique from ToddG, but I can't remember now.)
The change in technique was how initial contact is made with the gun when forming your grip. Initially, I used the same technique that I carried over from 4 o'clock carry, which is probably most easily described as just grabbing the gun. But, with a heavily canted behind the hip IWB holster there is so much room between the front strap and the belt that there is no risk of hitting your knuckles on the belt. This space is significantly reduced when switching to a straight-drop AIWB holster. One option is obviously to go to a higher ride-height, but this also comes with some loss in concealment. The other option is to alter your draw technique.
Instead of attempting to precisely place three fingers of my strong hand through the small space between the front strap and my belt, I make contact with the tips of my fingers on the outside grip panel and follow the grip around the front strap. For me, this eliminates any chance of my fingers hitting my belt, and it also results in a much more consistent grip on the gun. Obviously, if your fingers are thicker than the space between the front strap and your belt, then this technique isn't likely to help without also increasing ride-height.