Well, in my mind boxing out is a rebounding thing, it's not a defensive thing (you still try and box out if you're going for an offensive rebound, it's just harder to do) and i do believe that boxing out is a part of rebounding in game mechanics as well.
Maybe that's where the confusion was coming in to it?
Either way, to try and put some sort of a summary on things (or at least my view on them) there are probably a lot of factors for offensive rebounding in particular with rebounding skill being the major winner by far but shot selection, opponents rebounding skill, players position on the court when the shot goes up, even stamina later in the game would all come in to play i'd say. The only one that you can really control here is rebounding though.