It's a matter of preference really, I mount mine just a little bit back, -2 sounds good, i think thats where mine are but a lot of people would just put them at true center especially with it being you pure park ski.
I find that mounting a little bit back and closer to where the turn radius is most effective can help with carving off a jump and makes it easier to spin but mounting true center could make you a little bit more stable landing or taking off switch but in reality, look at 2cm on a ruler and compare it to your ski and ask your self how much difference will that make to how stable i am?
I'm sure they'll ski awesome where ever you mount them.