Sorry, just now read the second page. I think what they mean is you want to sit correctly with your heel, hip, and shoulders all in one line but rather then rolling up on your pelvis like a hunter you want to sit deeper in the saddle, more like on your pockets. Back is still straight and shoulders are back but you are opening your pelvis and sinking into the saddle. It's hard to describe but you'll know it when you get it because it's a completely different feel.
I tend to roll forward on my pelvis when he gets up which is the opposite of what I should do. By sinking into your saddle you'll also find it easier to get him to use his rear-end rather then his front end.