RE: how much shim to change down thrust?
Hi Rob, methinks you gotta move the CG back a little more then. At least that is easy to try. You could temporarily put on some more sticky weights, or take off the TT spinner for a couple of flights to see if you are going in the right direction still.
If it were too tailheavy already the elevator would probably be too sensitive, which it doesn't seem to be....?
Ernie