Tristan It was more of an psychological abusive relationship rather than a physical one, thus the sex position could have little to do with it. Not to mention, the abuse appeared to be spouting from Ben's fear, compulsive nature and paranoia rather than the need to dominate. Therefore it's entirely possible for Ben to be submissive (or be a bottom) while maintaining the abuse. Maybe he used his own insecurities to persuade Davy to abide his rules.
Maverickgirl31 Hmmm...there isn't enough information about Ben and Davy's sex life for me to make a good guess. Although you get the impression that every part of Davy's life was inhibited...so maybe he always wanted to explore that said but never got the opportunity with Ben...but who knows.