Ideally, with the rudder set straight, if you draw a line from the rudder post to the servo pivot point, both the servo arm and the tiller arm should be at 90 degrees to that line, preferably facing the same way. The connecting rod should then be the same length as the post-pivot line. If the servo arm fouls the panel, it is permitted to shorten it and use a hole nearer the pivot point. This means drilling a new hole to correspond in the tiller arm. Expect a servo throw of about 45 degrees each side. A rudder throw of this size is usually more than adequate.