You will need to move it around a little to see what it likes. My car likes 13.0 and will slow down a little on either side of that.

I would be OK with lean at idle, with a big cam the overlap really messes with the air mixture readings at low RPM. My car is fuel injected and I can idle it as lean as 17:1 on the gauge but my target it set at 15.5 and it idles great like that.