I think I know why they sit like that
After seeing so many posts on the Siberian Sit, it just occurred to me that maybe they sit like that because their hind legs are taller than their front legs. Apparently this is because they are built for jumping. I've noticed mine walk funny because of it, and when they sit like normal cats, look super awkward. I wonder if it's just uncomfortable for them to sit like a standard cat, so they have to splay, sploot, and sit on their butts. It also may explain why they spend more time on their backs than other cats. What do you think? In any case, show us your funny sits pics :)