It seems that Male_On_Herm is aliased to Herm_On_Male. It clearly is not the same thing. As I read it, the first gender mentioned would be the one verbing the 2nd gender.
post #332621 - A male penetrating a herm
post #279280 - A herm penetrating a male
I seriously doubt that searchers of one tag would be looking for the other tag.
Female_On_Herm is also aliased to Herm_On_Female which I suppose makes a little more sense (and possibly the origin of the other alias?), but still as I read it the first gender is the actor and the 2nd is the recipient.
Do we need better language for what the tags are trying to describe? Danbooru seems to prefer Gender_With_Gender, but that then makes the partner's positions ambiguous.
Updated by Furrin Gok