The Varimagni has its own adjustment. This works in conjunction with the vf diopter adjustment.

IMO the most convenient way to make the adjustment is as follows:

With the Varimagni not mounted on the camera (i.e. using it as a low power telescope with a right angle bend in the tube) switch it to x2.5 and focus it so that objects approx. 1 meter away are in focus. (Wear your glasses if you need them for distance!) This way the focus is the same (or very nearly so) whether it's switched to low or high power.

Then use the diopter adjustment on the camera to focus the Varimagni when fitted to the camera.

You can leave the diopter adjustment alone & just twist the Varimagni focusing but if you do this there is likely to be a big difference between the low & high power settings, which is annoying.