Why wouldn't they be able to do different positions though? You do realize that smaller tops can easily do most of them, right? In some cases, it might be even easier for the shorter guy to top...just saying.
And I'm not sure how his ass getting wet in heat has anything to do with anything? There are actual girls irl who exclusively top and trust me, they get wet just like any other girl. They still don't wanna be penetrated though. And since sex isn't just a physical thing, but also psychological.
This means that even though your body might've been technically designed for one specific type of sex, if you don't like even the idea of it, your brain will affect your body, making something that should be pleasurable, an agony instead. And I feel like way too many people dismiss that.

it's not my cup of tea (this seme i mean) ┑( ̄Д  ̄)┍