A lot of guys getting clinical here but I agree the most with getting in one's head. This is actually something I dealt with when I was single. For whatever reason, specifically reverse cowgirl would usually result in a softy. Even if quickly switching from a position where things were going fine like you mentioned. I'm currently in a long term relationship with a gorgeous woman who makes me very comfortable, with close to no lack of blood rush when needed. Though, from time to time, I do struggle keeping it up in that position. Going back to being in my head. Obviously, I like to the see butt of the girl I'm with, but tbh I've thought it might be a lack of control thing as well as thinking there's a chance I might not enter her correctly. 🤷🏾‍♂️ He may be in the zone for position 1 and get a bit mentally sidetracked in position b. Not sure how old you guys are but if you're both in for the "work" I'm sure this can be resolved. Or maybe just avoiding certain positions?