Holley fuel idle trim setting

So I just started tuning my fuel idle trim on my 4 barrel holley. I hooked up a vaccume gauge and started 2 1/2 turns out on each side. I adjusted inward leaning out the mix and the vaccume increased. I kept going until I was at a half turn on each side. With that I'm pulling about 13 inches of mecury and it seems to run ok. That seems like a really lean mixture though....I'm new to carb tuning so maybe I'm wrong. It's a 1970 340 by the way. Any advice?