Yes indeed, I realized that I understood the debt ratio calculation wrong, but @timcliff helped me with that.
But this still doesn't change my conclusions so far.
The sbdpotato and burnpost interaction is only complementary when burnpost is burning SBD.
Since there is only STEEM to be burned by them (debt above 10%), they are slowing down the STEEM supply increase, Wich make the debt ratio recover at a lower pace. So it slow down the sbdpotato effect on the debt.
Still, reducing supply won't affect the price up. It might help to avoid it to go lower, but don't push it up.