My Rising Trot - It Needs Work... Big Time!

After looking at the video I posted and posting a critique of my riding on the horse forums (here), it appears as though I have a chair seat and my rising trot needs A LOT of work. I couldn't agree more with that one of the posters said- shortening my stirrups and bringing my leg back and underneath me. Doing so will make posting easier and more comfortable for both me and the horse.

Goal: fix my legs, seat, and therefore my rising trot!

This is a quote from an article I found so that I may reference back to it as needed:

Problem: A Heavy Seat
Culprits:  Hunter Riders and Dressage Riders
"I often see riders posting straight up and down in a chair seat rather than forward and back, and that causes them to land heavy on the horse's back," says Scott. This position also makes it difficult to balance, which causes hands to bounce and jar the horse's mouth.

Cure: Stiffness is often the problem. For the hunter rider, pick up the posting trot, and with one hand grab your horse's mane about halfway up the neck (make sure to keep your shoulders square). This will pull your shoulders forward to the correct 30 degrees and help you feel how to land in the saddle softly. Maintain this position for 15 to 20 strides and then let go of the mane. Repeat if you fall out of position.
For the dressage rider, a stiff, closed hip angle is usually the problem. Think of the posting trot originating from a kneeling position instead of a sitting position. Your knees should point to the ground, and your hip angle should open as you rise and close as you sit. Think about someone pulling your belt buckle forward as you rise and then pushing it back as you sit. Don't let your knees shift around. Keep them pointing toward the ground as best as you can.

From Perfecting the Posting Trot