ketch lead

That's true...why is the lead measured then as a percentage of DWL. As a percentage of CE height it would tell us more.

Perhaps because it is clear parallel line with lead?

 

The depth of keel also affects the offset. A deeper keel has a larger movement to windward than a shallow keel.

 

I originally advocated using heeling arm, Gonzo, but I'm not sure the center of drag through the water moves to windward much as the boat heels, and that's the real issue. It might on a narrow boat with a very large ballast bulb, such as an IACC boat, but the additional stability from that bulb will likely mean a taller rig, so I think measuring from the waterline still works in that case. Either way the reasoning would be more valid than using a percentage of waterline length. If it were then determined that other factors prevent all boats from clustering together we could do some interesting and meaningful analysis.