Raising the rear of the scope with shims has the effect of lowering the sightline on the target meaning the crosshair is lower on target
This means you will raise the rifle to align the crosshairs on your target, thus you wont need as much adjustment on the up/down turret (elevation, the other one is windage)
Adjustable mounts do the same thing , in a better way
We are talking about inserting a shim in the ring base between the scope tube and the mounts base.
You probaly didnt need this on the EV2 as I think they have a slope built in to the scope rail, giving the same effect as shims or adj mounts
Its a safe bet the s400 hasnt got this