This may help but I would try doing no stirrup work and sitting the trot also doing bareback has help me not lean so far forward.
When your training think about sitting back to the point where your not straight up but almost leaning back a bit. Aim to look like a grand prix jumper right before a jump. That's what I imagine and my whole seat has improved.
Do a lot of trot and while your doing that work on sitting up. You can even do it at a walk and that be all you focus on.