Chiming in to give an official word on the issue.
Size is completely random, It cannot be bred for. Having a size in the genealogy of a cat does not mean you have a greater chance to get more sizes with that cat in the future. It's a completely randomized stat.
Also as a general reminder, please be kind and courteous to each other. We encourage healthy, respectful debate, however bashing, rudeness, and insults are not okay and I've noticed a few people in this thread being a little unkind to each other. Play nice! Thanks.