first of all skis are measured in the metric system, ie centimeters and millimeters. depending on recommended mounting points and personal preference. if you haven't skied much do what they recommend and pay someone else to mount your ski. if you are interested about learning how to mount skis. go watch them mount your ski, ASK ALOT OF QUESTIONS, get off newschoolers. if you think you'll get good info here and not get trolled you are high or just stupid.
but in my opinion i prefer my skis one CM back from center, i am also not a park rat, i ski mostly steep powder, cliffs and tree jibs, pretty much anything but groomers. i ride fat skis as well.
if you are a park rat. center is legit imo. then you ride the same going both directions. but i know little about those twigs they call park skis.