The rudders should be parallel or close to it. Best if Toe-in just a bit, but certainly not 15 degrees. 1/8" to 1/4" toe-in is likely optimum.
If they have aluminum rudder castings, the tiller arms bow inboard and the tiller crossbar is shorter. Mount the rudders on the opposite hulls and connect the tiller crossbar... you get highly Toe-in rudders. This could be the simple answer.
Sure you have a Getway tiller crossbar? The Wave crossbar is shorter and does not have a hiking stick hinge.
Older tiller crossbars that were used on the aluminum castings were shorter. The EZ Loc rudder system uses a longer one.
I highly suspect a miss-matched rudder system / tiller crossbar is the issue.
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