Every 7 kittens born, 6 are normal size and 1 special size!

[anna Acanthus]

Interesting … so i thought i'd compare and found that viewing my whole collection i have at the moment about 2,180 lives and boxes of which 140 are special sizes = 1/15.5 specials.

Of course this isn't at all the same test case as your's, (i've been breeding since March 2011), the Mega, Bigga and Petite were introduced January 2013, so forgetting the Teacup and Toy which were the original special sizes, my proportions for these are a bit different from your's :

Mega : 7
Bigga : 13
petite : 17

I haven't sold very many of theses 3 sizes and in general i don't menagerie a special size, but i have menageried loads of normal sizes, at least 1,300 i'd say, which would imply that my overall special size incidence would be even less frequent than 1/15.5 but as i can't remember how many Teas and Toys i've sold or given i can't make a very sure estimate.
Impossible also to make any overall estimation as from January 2013 in my case.

So anyhow, the divergence of your and my statistics suggests to me that the incidence of Toys and Teacups was maintained and the 3 newer sizes' frequency was added when they were introduced, rather than the 5 sizes being spread over the same frequency of special size incidence as before, hence the augmentation .