Here's a thought - he has poor posture. Stretch before riding. Do the pelvic tilt to change the angle at which your buttocks and pelvis engage the seat.

I'm saying this because that is aa RADICAL seat tilt. You are trying to use the seat tilt to make up for some other ergonomic deficiency. It would be better if we could see a profile view of you seated on the bike, rather than just the bike.