Go core centre, that way you're in the middle of the rocker. If you go too far back on these you'll have barely any contact point behind your boot when you're out of the pow. Don't forget there's only about 100cm of ski on the ground with these bad boys.
mounting back 1cm is not going to make any noticeable difference to powder fun, go in the middle and enjoy that balance.
Core centre is still 1.5cm back from the true centre of the ski so you're not dead centre anyway.