Adjustable Vacuum Advance

I see it now. When the screw is turned in CW the whole way the spring is at its most relaxed. A relaxed spring may lead to pinging under load, and in that event you turn the screw CCW. Looks like the best setup would be earliest vacuum possible without pinging, or as far CW as possible without pinging.
Correct. The tricky part is the part throttle loads. Too much vacuum advance under light load can feel like 'trailer hitching' but that's rare.
Don't know if you went to the linked thread but this is an example of how turning the adjuster counter clockwise shifted the vacuum advance.
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Because the purpose of vacuum advance is to add timing for low density fuel conditions, we can say that there should be no vacuum advance when the mixture is rich.
So an engine that needs full enrichment at 10.5 in of vacuum would need the vacuum advance to go to zero around 10 or 11" Hg. If we know the power valve or step up opening point then we can match the vacuum advance to be in the ballpark.