The vacuum retard is for emission control and is only active at idle or
heavy deceleration. When you open it wide, no vac = no retard.
You can set the overall advance for whatever you want.

I'm not sure how the vac retard improves emissions at idle because it
makes the throttle more open for a specific idle speed. When you
advance the ignition the idle speeds up and you have to close the
throttle more to get the idle to slow down to where you want it.
On the other hand if you change the overall advance to where it idles
fastest with the vac retard connected, your open-throttle advance will
be that much greater (7-10°) compared to what it was at idle.
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George Downs, Bartlesville, Oklahoma, Central US