Here is a article on rock sit vs tuck sits. I accidential taught Justice to Rock sit. It caused alot of issues down the line when training for competition. I had to retrain his whole sit behavior. Not fun. Diva had a heck of a time learn to tuck instead of rock . We did tons of skooch sit(half step forward sit) to get the muscle memory down.
http://www.clickersolutions.com/articles/2001b/compsits.htm
I'll see if I can get video of it.
Maybe it's because it's 5:25 in the morning, maybe it's because I am just daft, but I don't understand the difference.

I'll re-read it again and see if I can understand it better.
