For some reason I think Kallus is the type of guy who’s all cold and untouchable in business but is a bit on the masochist side on bed (does this trope has a name?). And Zeb may be easy-going to his casual colleagues/friends, but I think he is more reserved about his feelings and stuffs. If he (and his partner) feels comfortable enough, he won’t mind showing his more dominating side.
Anyway, I think they will be creative and rotate positions to try new stuffs, and topKallus is great too. So here’s a pic. I wanted to draw Zeb wraps his legs around Kallus’ waist at first but his toesies are too weird to draw so have a wall sex instead.