100% mast max down haul .it will throw air out the top instead of throwing you over the handle bars .
i use to use 30%-50 mast for a long time

.85- 100% is more flex and gives you more time for recovery .
softer ,more flex .longer harness lines might also help.( better flex is more forgiving)
If you feel your going over ,don't freeze ..as most do ..let go your power hand .or push it away.
a impact vest is good ,if you catapult a lot ..
i don't use chest harnesses .i feel having the weight of your sail at the hips will get more of your weight to you feet .and it's lower ....
plus I've got a **** back ,and can't use any hook above my navel.
it comes down to technique ..really ...but those things may help ...

i hate catapulting ...luckily haven't done one for quite sometime ..touch wood.