skillet92,

It partially has to do with the upper wing being offset forward (positive stagger) in relation to the lower wing and the fore - aft taper in the ailerons at the point of attachment. If the wings were at O° stagger and the ailerons were flat plates then you could mount the connecting rod at the same point top and bottom and they would move equally. As you move the stagger foreword the geometry changes enough that the attachment points need to be adjusted to get equal movement of the ailerons. The pictures show the points and brackets used by Waco. For the model, get a couple of toggle bolts of the correct size, take them apart and you have the brackets ready to mount.