You have a very nice, solid leg. I love that you allow your heels to do their job, which is anchor you in your tack. Your leather are at a perfect length for you, you have stabillity and are more than capeable of supporting your upper body with your lower.
Your seat is exactly where it should be. Low to your tack, and over the center of your saddle. You allowed your horse to lift you out of your tack, instead of you thrusting yourself out and forward.
You have a great back, love that you are looking up and you are with your horses motion.
The only issue is, you are over using your upper body, drastically. The only time we should see a rider with that cosed of an upper body, is when we are seeing riders doing 4'0" or bigger.
A rider should allow their horse to close the angle for them, instead of collapsing their upper bodies so drastically. Your hip angle should be much more open than that.
You definately do not need to be using your horse as a crutch for balance - you clearly can support your upper body on your own, via lower leg stabillity - stop relying on your horse, and don't fall into the pitfall of being a percher/poser over fences.
You also should be working on the automatic release. George Morris rants about this often, he created the Crest Release only for beginner riders - riders who cannot support their upper bodies with their lower, so that they don't interfear with their horses job over the fence.
Challange yourself and break yourself out of this habit.
Here is a critique that GM gave in one of the PH magazines you might find intersting: Form Over Fences