Ray,
This is what I think too. I have been running with head shims from 0.3mm to 0.5mm with 30%. One thing I check all the time so that I have not gone too far is by reading the plug. I will try to use less shim as possible on our BRB without eating plugs.

For Hong Kong, I use 0.4mm for running in, then 0.3mm
For Thailand, I used 0.4mm (0.3 , the wire pushed in really bad)
For Sydney, I used 0.3mm

If you have a Exergen temp gun, you can use Temp as reference. But if you use most other brand, the temp could be off by 20 celius.

My suggestion
Tune for performance, Read Temp, then Read plug ( Exergen Temp gun)
Tune for Performance, read Plug, then Read Temp (other Temp gun)

Chris