You put shims on a scope mount?
I put the shim between the base and the action.Shimming the back of a one piece base gives you more elivation adjustment , shimming the front gives you less.
Once I have it figured out how much is needed the action and screws get a little relese agent and the base is JB welded to the action with the shims in place. The screws are tightened only so contact is made and let harden. After the bedding material has hard the screws are touqued down and exess is trimmed off.
If you look between action and the base you can see the bedding.