It’s not about similarity, the Kinsey scale just measures your level of attraction to people of the same or opposite sex.

This starts getting more into “what parts of the opposite sex are you attracted to, and how is the other person presenting themself.” Femboys present femme, so a femboy liking other femboys might be attracted to their feminine characteristics. If that’s the case, they’re likely to score closer to strictly heterosexual than a femboy who is attracted to the masc characteristics of a bear. On the other hand, maybe the femboy just really likes the idea of getting railed by another femboy. Then, they might even be more strictly homosexual than the femboy who’s attracted to bears, but refuses to be the receptive partner to them and always tops.