Hi Tony

Thought this extract from tuning guide for Nacra F18 might be helpful, different boat, same principles apply..
"Moving the mast aft decreases power and makes the catamaran easier to handle, hence further back in heavier winds. Also the lighter the crew, the further back the mast and visa-versa.
Also moving the mast aft, allows the center of effort on the sails to move further aft and so will encourage the boat to point higher. BUT this might mean that you feel “weather helm” through the tiller, if so, “tuck” the rudders further underneath the catamaran by adjusting the screw thread on the rudder casting. When sailing upwind, with two on trapeze, you ought to be able to rest the extended tiller on the top of your index finger and the catamaran should slowly climb up into the wind."

Hope this is helpful.

What type of lock-down system are you using on your rudders?

Cheers

Andrew