If the situation you describe is the general case (and I would think it is) then those two varieties are separate species are they not?
The Hovind-ites aren't going to agree. "a dog is still a dog"
I guess the exception would be the small male impregnating the large female. I can't really picture the mechanics of it happening (!), but the offspring and parents would most likely surive. I imagine it wouldn't happen in the natural though, so the exception fails.
This isn't about Genetics, so I suppose it's off topic. But I don't think Creo's realize it stuff like this that can result in speciation.