I'm considering purchasing an asymmetrical spinnaker. I've been told that the standard way to determine the length of the luff is that it should be 100-110% of the I dimension. But I've never heard of, or been asked, whether the boat is a masthead or fractional rig, which I would think would make a great deal of difference. Can you explain how to determine the luff length of an asymm spinnaker on a fractional rig??