>>15334tbh I also do it and usually it's even the top not the bottom. But I wouldn't worry, I think it's more of a first-person perspective, like in games. Just combined with some sort of relation because let's be real, if you really obsess over two characters and love them you can relate to them to some degree, otherwise you wouldn't understand them and get all those ideas when you think up fanart motifs and fic plots for them.
And sex between two hot and relatable characters is of course arousing too, so a part of your brain always participates in some way, this doesn't mean that you're trans or even yume.
As for the trans issue I believe that it's mainly caused by sexism. Many women simply feel bad for being seen as sex objects by many men. Boomers in particular can hardly mention a fucking female politician and scientist without first clarifying how fuckable or ugly she is. It's not about comparison IMO but disgust. One of my main fears as a teenager wasn't to ugly but to be attractive, and not because I feared rape but because I feared objectification.
Plus, one of the advantages of gay sex is that the sex role depends on the personality, not the sexual organs.