all the retromingent animals I
know of are female. I think retromingent males
would find copulation extremely difficult.

Aristotle wrote that male lions are retromingent and perhaps that is why the rumor persists to this day. But this photo of lion's mating would seem to corroborate your theory, wwh. Go to:

http://www.africanlions.co.uk/mating/thumbnails/pic/lm1.jpg