Thanks for the input guys. I will try tightening the leg straps, I haven't been doing that very much. But I thought the whole advantage to having a seat harness(especially when your a beginner) is that its doesn't ride up. Even once you have experience, you will be boosting airs which is going to pull up on the harness, it won't ride up then? I'm a little disappointed but hopefully it gets better.
Its body position and skill. If you attempted the same tricks with a waist harness, guaranteed it would be up around your armpits. Boosting airs requires you to keep your body weight through your arms/bar and body position somewhat "perpendicular" to the pull of the kite.
If you want to see how "messed up" your current style is, make the switch to a waist harness. You will hate it and it will hurt, but any issue is just a reflection of current skill/technique and not the equipment.
IMO, stick with the waist harness as long as you can and focus on all the basic techniques such as front side/toe side riding/toe side down loop transitions/pops and basic jumps. Your kite skills should be automatic in that you are looking around you and where you are going instead of looking at the kite... Flying the kite through the feel of the bar. Should be able to get through the Progression Intermediate skills on your seat harness... Then make the jump to waist harness and start working on your front/back rolls/unidirectional etc.
Wedgies are natures way of saying you are doing it wrong