Mk2 castor angle

Can someone please explain why the shimming and position of the spacer can be very different on each side of the car. Instinctively I would have thought it be be almost the same?

To allow for the camber of the road surface. I was talking to one shop recently and he mentioned that a lot of American iron (private imports) coming here had the new owners complaining that the cars would not drive straight, due in part to the castor angles non adjustability.