Thanks for the reply, I should have quoted. I was referring to the fiberglass method noted.
It seems that using a shim (or two shims front and rear) only UNDER the scope body would still cause a tilt of the scope body in relation to the top strap along with uneven pressure there. Understood that it is a very small tilt and that many do it successfully but it is why I don't use shims. Adjustable mounts and the Burris system address both the top and bottom of the ring.