I agree with the other posts. You could use more angle in your leg. That second to last picture is very telling. Your crotch should stay behind the pommel when jumping. Instead of standing in the stirrups, maybe try shortening your stirrups a hole and practice letting the horse's jumping motion fold you into a proper position over the fence. If you fold more, it should allow your arms to come more foward to give you pony a bigger release. Back is flat and you're looking ahead which are both good.