The curious case of The Magic Penis [orgasm problems]

My girlfriend has been with a fair amount of partners, around 15. But only one of the first of these guys has ever been able to make her orgasm in multiple positions instead of just on top. However, when she slept with him again years later, the same result. So only 1 out of 15 was able to achieve this feat. So it wasn't just a one off, and the other guys were all of mixed age/ability.

Please give me your thoughts reddit, is it penis shape/angle? technique? stamina? whats going on here? And maybe how could I go about solving this most mysterious case....