To allow further descriptiveness to works involving femboys, I propose two new tags to define whether a feminine male character is a top (penetrator) or bottom (penetratee).
Definition
femboy_top - Refers to when a femboy is penetrating another character or object, or is depicted to desire to do so (eg. dreaming about it or explicitly stating so).
femboy_bottom - Refers to when a femboy is penetrated by another character or object, or is depicted to desire it (eg. dreaming about it or explicitly stating so).
The exact definition can, of course, be changed and even the tags can be renamed if you have better ideas.
Implications
Both tags simply imply femboy and male.
Just FYI I've never even seen how tags are supposed to be introduced so this may be way off target lol.