I don’t pretend to be an expert on guns or shooting, but your question is interesting. So, I’d like to venture a comment. As to changes in stock dimensions over time I would concur that it does appear that stocks are getting longer and flatter. My guess is it has less to with physiology and more to do with people learning more about shotgun shooting. I will credit the English with starting it all. Of its face it casually looks as if our cousins gained an early grasp of controlling impact and recoil mitigation.
As to how much drop one can tolerate, I’m not qualified to state for everyone. I know what is too much for me. I learned through painful and expensive experience. I’ve had to learn not to buy a gun, no matter how wonderful it might be, whose stock was obviously not well suited for me. I think avoiding excess is the key in length, drop, or cast.
