Hi
Based on my P235 rig I would recommend getting a copy of Sail & Rig Tuning by Ivar Dedekam and going through the process it outlines. I also found it useful getting a Loos gauge which although expensive means you can do quick rig tunning, achieve repeat settings and use it each year to check my rig.
In general with sweeped back spreaders the cap shrouds don't need to be over tight to get the correct mast bend.
Although on a fractional rig the backstay doesn't have a huge impact I have found it does give some improvement in foresaty tension.
I would also consider meansuring the lenght of the forestay/furler.
The above is based on my experience of playing with my rig and reading different set up guides from mast and sail manufacturers
Regards
Andrew
Jago
Parker 235/04