Possibly to account for futanari and male equivalents, there's no good solution for these special cases, since yuri and futa are mutually exclusive. You could use misc for hetero stuff and use male/female for homosexual stuff, but that way you'd have the male with futa stuff mixed in with the hetero stuff. Simple enough to fix by including/excluding futa in the misc search, I guess, at least much simpler than the hoops you're expected to jump through to get results approximately close to futa with female. The other solution would be to have separate tags for receiver and provider, but that would never happen regardless. Feel free to propose such a change on the forums, though it most likely will be rejected.