All I know is tie a bungee from the beam up to the mast at a point well above the tack of the mainsail. That deflects the blocks and prevents the jib leads from snagging. I have mine tied (on a nacra 5.2) from about 1/4 on the beam to a metre above the mastfoot. It used to be tied lower, but the jib leads got caught on the mast rotator when that was out at 90 degrees or more. I fitted a small thingamyjig on the mast for the bungee to go through. No snags since!