Vacuum advance can adjustment

The adjustment changes the preload on the vacuum diaphragm. Not the amount of advance. So you are adjusting the amount of vacuum required to add the advance. Not the number of degrees advance itself. That's true with all the vacuum pods I'm aware of.
Also - manifold vacuum won't give you much of anything at idle especially with a cam/package with limited vacuum. IMO that's a mistake - use ported. And add initial if you need to.