Cool stuff,
You might want to also add some form of bracing behind the shim, something .5mm that slips (wedges) in between the shim steel and the ply-edge.
This re-enforcing addition should prevent ball-dents.
In fact, if you cut the shim pattern with some extra folding tabs, you could fold the shim to hold the .5mm backing in place....
Then it becomes a 1-piece drop-in soloution.
MM
