Man I learned this the hard way too, three layers seems about right for how frustrating it gets.

Did I ever mention I once chased a phantom vibration for three days before realizing it was my own coffee cup rattling?

yeah that IR trick is wild once you see it work. I've been messing with one of those cheap chinese IR preheaters for about a year now and it's a total game changer for removing conformal coatings too. the way the heat penetrates instead of just blasting the surface makes a huge difference. hot air just bakes the outer layer into a hard crust while the bottom is still solid. but with IR you can dial in the wavelength to match the plastic's absorption and it softens the whole mass at once. only downside I've found is you gotta be really careful with sensitive components nearby since the IR heats everything in its path. I've cooked a few tantalum caps by accident. still I'd take that over fighting with solvent and scrapers for twenty minutes any day.

Read an article that said most cabinet hinge problems are usually just a 1mm screw length difference. Sound about right for your situation.

Tbh the real wild card here is your steel's grain size before you even heat it. 1095 can be super picky if you didn't normalize it right, then even the perfect oil temp won't save you from a soft edge.