Here is the answer from chip as to the way the sail is cut.

The new fabric FLEX13P from Dimension Polyant is the best of the cross-cut fabrics and works well with a your boomless system. Having the clew bar loads the foot of the sail not just at the corner with loads radiating out it's entire length. We don't want to load up the clew in the wrong direction, that will cause delamination. If you had a conventional setup (boom) then the tri-radial is more appropriate.