Okay, found another. I'm a little forward in this one too, as I am off her back a little to let her find her way (She is very, very green and not broken in long + first time over poles) - But would you agree that my pelvis looks better in this picture?
When working with a young horse the rider needs to assist the horse with rising its back. Especially in cavalletti. This is accomplished by sitting in the saddle, not leaning forward, squezze both of your calf muscles inward...this creates impulsion, and then bring your calves upward, this will cause the horse to rise its back.