The Nacra's with bowfoils experience the opposite effect when sheeted hard. The bows toe out slightly. The foil eliminates the horizontal component of the load that would normally be exerted on the hulls by bridal wires. The rear beam however, bends considerably when sheeted hard on centerline ~1000 + lbs of tension. My 6.0's all toed out about 3/4" (at the bows) more under load then when relaxed. I believe it is most important to have everything parallel sailing downwind or in light air, so that is where I had it set. Once you have the main sheet on hard, you are flying a hull anyway and parallel is less important. Note: the rudders tow out slightly under load also so you might consider setting them toed in 3/32" when the boat is relaxed.

Sail fast,
Eric Anderson