AIWB is flat out more complicated than strong side is. That’s not a bad thing, it’s just a different ball game and I think that’s the cause of the issues you’re running into. You’re taking what works well strong side (short holsters/stiff belts) and trying to translate those to AIWB.
I’ll say that the certum is not my favorite AIWB holster, and doesn’t conceal particularly well for me in that position. However, having a thin belt (tenicor zero) a g17 length holster, and an appropriately sized and shaped muzzle wedge make that holster conceal better than a g19 length holster with a stiff belt and no pad. If strong side is working well for you there’s no real reason to switch, but if you are interested in making AIWB work for you, you’ll probably need to give a longer holster and a muzzle wedge a try.
Jon Hauptman of PHLster has compared dialing AIWB carry in to fitting a prosthetic, and that’s a good comparison. If that’s not a level of trial and error that you are interested in, and you get an acceptable level of concealment from strong side, just keep carrying strong side.