Barrel Length for AIWB

Up until this point I've been carrying a 3" model 60 j frame revolver. I've carried it consistently for two years with a speedloader for a total of 10 rounds. I'm invested in this system with a Milt Sparks belt and strong-side holster which works for 3/4 of the year. My problem is the same as most which is that I can't conceal it under a t-shirt in summer. Whenever I bend over in the slightest the grip sticks out like a sore thumb and therefore I dress like it's spring/fall and then I stick out. So I figured I would look around for a smaller semi-auto.I went to the range with a friend last week and shot his gen 1 m&p shield. In addition we rented an m&p 2.0 compact 4". I shot all 3 with roughly the same accuracy, but the compact was definitely easier for quick double taps and follow up shots.My friend let me try on his holster at 3:00 and 4:00 with the shield and to my disappointment was less concealable (with the 7rd flush mag) while standing up than my revolver, let alone bending over or sitting down. I really don't want to suffer through another summer wearing light jackets when it's 95° outside.I began to search online to see what other options there are since I can't conceal one of the smallest handguns (with my wardrobe) on the market. It seems there were 3 options, pocket carry, ankle carry, and AIWB. The first two seem less than ideal in regard to draw speed, shootability, and capacity, with the size of firearm I'd be limited to. I tried AIWB in the past with my revolver but it was quite uncomfortable, but I read some "how-to's" and by just pulling up my pants an inch, it became quite comfortable! Furthermore it just disappeared! I decided to measure the width of my revolver and both the cylinder and grip are 1.2", the same as the m&p 2.0 compact.I think I've settled on the m&p compact but they have two different barrel length variants, a 4" and 3.6". One is roughly Glock 19 size and the other is Glock 26 size.TLDR; What is the longest barrel you can comfortably carry AIWB with? I sit all day at a desk job, so it needs to be comfortable in the car and at work. via /r/CCW https://ift.tt/2ZiwZan