The total travel of the scale table is approximately 0.050" at 20,000 lbs - I think I will ignore that! The shim goes under the opposite wheel, not the other dual wheel on the same side. I have put a couple of known heavy objects on the scale, it seems accurate. For my purposes, +/- 100 lbs it fine.
On my BF, the fridge, galley, and propane are on the right, but the head, furnace, and water heater are left, fresh water offset to the right a little. I haven't weighed the truck empty on each wheel, it may start that way for all I know.