TwigI skied 98% park on my test pair and was happy at true centre. The skis do feel a bit unbalanced on snow because you have loads of contact on snow in the tail and not much in the nose but given that I was riding almost all park and almost all rails that's still what i'd choose for the balanced swingweight. For a more normal ski use I think I'd go with -2cm.
You should note that (within reason) no matter how far back you go, you will still have more flat running length in the tail than tip. I haven't actually got my skis with me right now to measure but I would guesstimate the nose rise is around 25-30cm from tip to flat contact whereas the tiny tail is probably 5-8cm long.
I read your review on the ski and that was why I was considering mounting it further back. Since you said you skied 98% park I most definitely will be mounting them -1 because I will be skiing lots of off trail.
Thanks for the info