The system does jump around a lot. I tried basing it off of the way the vanilla game calculated the bi/homosexual change, but I think it’s far more obvious and triggers more with the multiple changes. I do plan on lowering the chance of sexuality shifts.
Regarding Futa, I do have them considered as males for the shifts (due to the penises) but may change that to allow player choice to toggle how they are considered by the system (male/female). I don’t know how to effectively make a third option on the scale beyond having it considered same the same as one of the ends.