I still will insist that positive Ackerman is a good thing on all pull-pull. It will not cause flutter when the non pulled line goes slightly slack when you move the surface off neutral as the air pressure keeps the surface tight against the line being pulled. IMHO pull-pull is so much more reliable and trouble free than push rods that there is no comparison for large models. Even most small models such as the little electric powered jobs benefit as there is a great weight advantage over pushrods with a much larger choice of servo locations to adjust CG placement without adding dead weight. Positive Ackerman can be obtained by having the attach points of the movable surface being aft of the hinge point (away from the servo position) or by having the attach points at the servo (away from the surface being moved) ahead of the hinge point of the servo arm. It is pretty easy to demonstrate this to yourself with a few sketches using a compass and paper and pencil to scale out the geometry.