When using the XL Spacers do you need to increase exposure? If so does any one know the additional exposure needed for the different size spacers?

It isn't that simple.

The relationship between effective aperture and aperture as set is: effective aperture = (aperture set) * (1 + (magnification/(pupillary magnification)).

For some of the lenses made for the XL pupillary magnification is around 1. I'm not sure about the 58 Grandagon.

Magnification = 1 + (extension from infinity position/focal length)

The spacer increases extension from the infinity position by its thickness, but since the lens is on a focusing helical it can be focused closer with the helical. That's why there's not a fixed relationship between the spacer's thickness and effective aperture given focal length.

Sorry it isn't simpler and easier,

Dan