I would highly recommend that if you shorten the rudder (originally designed as a "balanced" rudder), you should also implement a pull-pull configuration vice a single pushrod. Snipping off the forward leading section of the rudder (the part that attempts to "balance" the rudder) would then require more torque to properly control. I guess if you are a using high quality, high torque (pref. coreless) rudder servo (single pushrod), you could get away with it. Just my 2 cents worth.