I've experimented with anchor points all over my face! I settled on the same as you. Thumb under cheek bone. I also twist the pouch about a 1/4 turn towards my face and that has no detrimental effect on accuracy at all. If it's comfortable and you are generally hitting where you are aiming, just keep at it. You may have to tweak your aiming reference point, but as long as you anchor consistently the accuracy will come with practice.