It looks to me that in the first picture your leg has slipped back a bit. And in the last one too. In the last pic try putting the stirrup on the bulb of your foot and your heels down. Also try to lengthen your stirrups a hole or 2. And it you got out of the saddle a little it would help. Think of pushing yourself back over the jumps. Other wise your horse tucks nicely for being gaited, they most of the time have an off set tuck.