Holster is the key to aiwb carry, imho.
You'll definitely want to angle the grip upward to avoid some uncomforable situations lol. It might dig into your leg a bit instead of...well, you know. And after you sit, if you have to adjust a little, noone notices or cares because men naturally do that anyway a lot of times.
As others have said, I don't particularly enjoy kydex for aiwb either. It's not comfortable at all.
Even leather aiwb holsters can be uncomfortable. Try to go as minimal as possible with the holster to help with comfort.
I went through a cool dozen holsters before I got this one. It makes a CZ PCR disappear.
http://tuckergunleather.com/cover-up-plus-iwb-holster/
It's overpriced a bit, imo, but it was a gift and turned out to be the best one Ive ever tried. Fully adjustable for cant and height with two retention screws. I've bern carrying in this holster for three years now and have no complaints. You will have to periodically retighten the cant screw, though, or locktite it when you find the right height/cant combo. If you can find something similar cheaper, this style would probably be the way to go.
Haven't specifically asked, but Im sure
@chiefjason could make one for less.
As far as the tactical muffin top thing, I got nothin. I'm a skinny dude.
Edited to add: about loctiting that screw...a friend has loctited his, but I dont recommend it. I broke the clip on mine about a year ago and had to replace it. Much easier to do if it's not loctited.