The tighter luff curls more, letting you sail deeper; looser flattens for reaching. I don't know, cause I haven't done a lot of spinnaker sailing on beachcats, but having the head of the kite a foot or two from the mast would tend to allow more "slot" and might promote flow over the upper part of the sail. Just a thought. Oh, and like the other poster said, it keeps the sail lower too.