Lifter preload...more or less?
If you are shimming the shaft with .125” worth of shims you are moving the rocker up roughly that far, so, the pushrod side grows roughly that much as does the valve side. I did stock magnum rockers on a sft cam with regular pushrods and used arbor shims to set valve lash under the pedestal, a .010” shim gave me way more than .010” at the valve, was happy to get them within .010” to .015” of each other, took a lot of screwing around.