I've been skiing on my JMOs all season now and had the luxury of testing all the positions from dead center to 5cm back. I will say I am mostly tree and off-piste skier, so for me recommended is best, if not further back for powder. I just felt they had to much tail for really tight spaces when they were mounted more than a cm forward from reccomended. And bombing down the hill at 70 mph (very impressed with them at high speeds), further back was better for me as well. On jumps and rails center mounted
is best, but going to -2.5 made a negligible difference IMO.
Obviously you are more park oriented than I am, so I would say 2.5 or further back would be good. Maybe -3.25 if you want to use them to get into all mountain more. I also see no problem using them at recommended in the park- so it all depends on what you want to do and where you'll be taking them most.