Currently the reverse trap tag doesn't cover a fraction of what would be considered an androgynous girl. Some of them probably don't completely fit into the current criteria either, yet this is already the best tag we've got and there're no better alternatives. For example an otoko no ko wearing shorts would still get tagged as an otoko no ko, but I'm sure most of us wouldn't tag a reverse trap if the girl is wearing a skirt, even if her face looks perfectly androgynous. Often times if the girl doesn't look 100% masculine people will hesitate to use the tag, myself included, even though that's probably what users want to see. And obviously if you're not going to an extreme a reverse trap will still have feminine traits, just like many under otoko no ko still demonstrate masculine traits.
This is reinforced by its own wiki:
As a rule of thumb, if you can correctly tell the gender with complete certainty from the thumbnail alone, it's not a reverse trap.
This makes searching of androgynous girls extremely difficult. Some may suggest that androgynous girl works as an alternative, but it doesn't. Androgynous is already dominated by androgynous boys, so unless you filter out boys, your searches are going be filled with false positives. Plus androgynous on girls is not any less undertagged compare to reverse traps. It has happened many times where I searched for "reverse trap + a female character that's the definition of reverse trap" with little to no result, switched to "androgynous + that character", only to find out that there aren't any more results.
Is reverse trap underused and we need to expand its definition or do we need a more generic androgynous girl tag?
Updated