Isn't this only if you have to move the GG back to accommodate the Fresnel (i.e. so that the Fresnel is held in place by the GG) as you are changing the relationship between the ground image and the film holder?
I have several cameras with a fresnel in between the lens and the GG and there is absolutely no issue with their focus.
That's because the backs were designed that way to accomadate the fresnel. Take it out and the screen would be out of register in many cases.