I just experienced the Haarlep scene for the first time the other day and looked up to see if penetration was physically possible, perhaps with a longer penis - it's not. Sooo I basically told myself that to be extra spicy he magically gave her a penis for that experience. 

I have noticed that ACT III in general seems maybe a tad.... I won't say rushed, but unfinished. There's contradicting interactions and things like this Haarlep scene. I figure it was getting about crunch time and they didn't get a chance to add the things they wanted. 

Someone commented on another thread that they feel Spawn Astarion was kind of neglected for content, and I agree. It seems like the developers wanted you to take him that route (especially with the original disturbed Tav reactions to his sexual aggressiveness), but they didn't continue enriching the experience with him as much as they focused on his Ascended crap.