Single post in Your Guide to 90%+ Breeding Pairs

That example does nothing to prove that size makes a significant difference since it involves differing body shapes (minior and ditto have the same shape so it makes sense that they pair better than ditto + pokemon with different shapes) and isn't even particularly applicable to gendered pokemon. I MIGHT be able to believe that size influences ditto pairings, but I'd need more information than just "it does."