I just received my new Tokina AT-X 10-17mm Fisheye for my Canon EOS 40D. In the camera list I saw the upper rail setting is 98mm (lens set at 10mm). It seems like I have parallax here. Could it be eventually another setting? Is there anybody out there how could give me the correct setting please?

I am using the Nodal Ninja 5L

Also: what is the best aperture setting? I tried now f11, f8 and next would be f7.1 - but maybe I first have to resolve the before mentioned setting.