I'm 6.2' tall, huge, top, hairy, masculine, so I could never imagine myself in the female position, I like my boy to be comfortable with that, being spoiled, cared for, loved and taken cared of by his man.
I was in a 4 year relationship and not once ever felt like I had a boy or a girl role. We just existed together.
And I don't think your body size determines it. Physically, perhaps it means you are a better small spoon if you are smaller, but then we are equating femininity with body size which is not only problematic but wholly untrue.
When I was a kid my parents were very protective of me, so I'm just used to being treated like that.
It has nothing to do with wanting to be the female role.
I always feel like my partners play the more feminine role because they're extremely submissive. But I think that's mainly because I was more into the relationship than they were. I preferably would like a male-male relationship. I don't like taking a same-sex relationship and comparing it to a male-female relationship.