I think the potion-choice concept is an interesting way to get at this. But I don't think your potions really get at it.
The way I see it, for FtMs, the potion representing sexuality would be, you always see yourself as female, but others see you as male, including sex partners. The sexuality potion would be you are only female when you have sex. The gender potion would be you always see yourself as male in private, except you would see yourself as female when you were getting ready to go out, and everyone sees you as female in public, yourself included; but you would be male during sex.
But remember, the whole point is about ratios, so you wouldn't have to choose one potion exclusive of the others. Just how much you would like having each potion, in comparison to the others.
The thing is, when I put it this way, it changes my scores. I'd hate the sex potion, but would like the sexuality potion almost as much as the gender potion. So I'd be something like -10/50/60.
Curiouser and curiouser.