Recoil anticipation can be a hard habit to break or so I have heard. I`m not recoil sensitive as some people are but watching others shoot that are, low and left seem to be where they shot also. I have to make a few corrections the first few rounds shooting a semi-auto then I`m ok. Revolvers, no sweat. You might try to wear earplugs WITH the muffs, some people flinch because of the noise and the more that is muffled out, the better they shoot. Good that you have gotten back into shooting again --- it`s a great sport and I love it. Oh, as for your thumb I have no idea. I would have to see your grip to answer that one. Keep shooting!