In Origins, the Warden bottoms for Zevran, unless you modded. In DA2, you top Fenris. Can't you leave it up to imagination, or give us options?
I always assumed that Zevran let us do whatever we wanted. Playing a female Warden showed her on top and bottom in Zev's sex scene.
I rivalmanced Fenris, and in that scene you do initiate the first kiss, but I always thought he was the more aggressive one as time went on. That final scene before the boss fight where he kisses you... Mmm-mmm-MMM!
You make a good point about Bull though. As I've stated before, I know very little about relationships that work solely as Dom/sub, but the humiliation thing would totally not work for me. I never considered the romance from that perspective. I never thought of Bull as being disrespectful because he refuses to switch things up precisely because he feels doing so would be disrespectful to what the Inquisitor does. I can understand feeling that way though.
I feel like a lot of issues with Bull would have been avoided if they had made the Dom/sub thing happen because of Bull's preference. Like, if he had had a very troubling and deeply disturbing thing happen to him a long time ago, and being in charge sexually was his way of coping with that. But the way they wrote it, people have serious issues with him just assuming he knows what the Inquisitor needs. I think a lot of annoyance and confusion could have been avoided if he had said instead "It's what I need, and I understand if you're uncomfortable with that, but you needed to know before we get into anything serious."
Although, someone would have probably have still been offended by his lack of flexibility. But it could have been a good solution if they had written it well.