All of the 21s are high relief design. A few of the 22s are also high relief but the vast majority of the 22s are low relief. No 21's were made in a low relief.
Randy, your 21 is a high relief circulated XF silver dollar. The 22 is a low relief. You should be able to see the differences in the raised portions of the design. In doing so you have to account for the circulation wear on the 21.