I've recently finished assembly of a Skybolt ARF. It also has the lower ailerons driven by servo with the upper ones attached to the lower. Before cutting up the provided hardware for those connections (to use to make my more accurate rigging) I measured the whole deal and mapped it out on paper so it'd be easier to measure the "differing differential" movements.

I actually made full size cutouts that could be hinged and connected to work exactly like the ARF would work with the provided hardware. And took some pictures of the setup. I'm attaching one picture that shows the Skybolt ARF's "problem".

I'm also including a couple of "drawings" I made of the Ultimate situations. One is the stock arrangement. The other is the design of my rigging setup. I'm attaching two of the drawings that show the Ultimate "problem". The drawings were not as accurately done as the cutouts.

Since both airplanes obviously fly good with their stock rigging, it isn't exactly a big deal. But if you'd like for your Skybolt or 40s Ultimate to have ailerons that work like the larger biplanes (that use a servo for each aileron), then the pictures will show why they don't and how to rig them so they will.