It really comes down to personal preference. But, generally, no lean for jibs and park, and then whatever amount of lean is comfortable for you for freeriding. Again, that's only in general, and it really is personal preference.
I also have the cartel 2012. I ride as forward as I can stand. Right now they are set up for 2 turns past max setting. For me, the forward lean really helps with steep carving making them more responsive. Like others have said, if u are freestyle rider. Forward lean is not good for rails/boxes because flat base riding is more difficult.
I read somewhere that you should set it so that there is no gap between the highback and your boot, is that right/wrong/a good starting point?
For freeriding, when I setup my bindings that's exactly what I do. Lace up the boots, strap them in and adjust the straps, then I adjust the highback until it's just making contact at the top with the boot. Then I make small adjustments from there if necessary but usually it's about right on for me.