Well I can tell you from that drawing that something dramatic will happen to the helm. Just as it will if you tilt it back the same amount. It doesn't show the relationship between the center of the pivot point and the amount of blade is in front or behind. I've spent enough time messing around with various rudders and castings on the boat trying to find nirvana. I remember something about the "Aussie" way of setting up the rudders on a N6.0. Kicked way under. If what you show doesn't change anything why is it done? Why does Robbie change his?

To go back a bit none of this matters if the sail plan isn't balanced with the center board. I set my mast rake to get the boat to sail to weather with the jib and main sheeted firm and the traveler out a few inches and the rudders up. When I travel in the rest of the way the boat heads up. I gauge how much load I put on the rudders by how far out on the traveler is when I'm sailing without rudders to weather. Then I adjust the rudders to get the feel I want. Is this right - wrong? It works for me.

For what it's worth the Nacra rudders are seven (in the water) inches shorter than the Mystere's. The boat steers like a sports car with power steering and only time I ever get lee helm is when I try to go upwind with the chute.