Single post in Your Guide to 90%+ Breeding Pairs

Hello. I'm sorry if this has been answered somewhere all ready but I could not find it. If someone were to try to make pairs for breeding variants from scratch, for lack of a better term right now, is there a lower percentage for those types of pairs in general? (To clarify: not where both breeding partners are the variant, but for example, a male primeape and a female rattata) Or am I just having bad luck to get have the male and females from 2 diff OT and making pairs in the 30-50 percent range.