I was looking at the camera because I was on a circle and looking ahead. I’ve had some issues with my equitation when riding him. He requires a very deep seat and I find, especially when I canter, that if I’m not creeping up into a half seat (which causes lots of speed..), I develop a monster chair seat. I’m much more consistent with the trot, even though I tend to creep forward, my seat still remains quiet and keeps him pretty happy.
I don't think the chair seat is entirely your fault.
Since it's a jumping saddle with jumping length stirrups it makes sense that you can't keep a deep seat. Now if you had longer stirrups then you'd be much more readily able to sit deep. And it's easy to push your seat out of the saddle if you're jamming your feet forward.
In the canter photos I almost feel if you gave him just a little more rein, you wouldn't be nearly as "pulled forward" which may help with your creeping leg too.
This is just my opinion though. You're a wonderfully balanced rider
You're doing great for what you're working with :)
I wish I could give more rein! His owner and her friend (who she takes all advice) insist that I do not give enough contact. I have grown up with very light, forgiving hands and its very weird to be told to give so much contact, but eh - I will ride the horse the way the owner wants. He doesn't seem to care. BUT I rode him by myself today and got away with light contact because I wasn't being watched. ^^