Stop in for a cup of coffee

Does anyone have any good advice on when the vacuum advance should start to pull in? My car at idle pulls about 13-14hg. When I put the vacuum pump on my pod it starts to move at about 15.

If I remember right I need to know how much vacuum my engine pulls at cruising speed, but once I get that figured out, then where do I set it to start pulling in?
Vacuum advance depends a lot on the engine. Some come in at 6 or 7" of Hg, and others don't add any advance until 10 or 12".
It depends on how much the combustion slows under leaner part throttle conditions vs. near wide open throttle high load.
What engine and mods?