That's about what I was thinking.
So depending on the vacuum advance's internal spring, it may or may not be contributing anything at idle. I posted an example a little while ago - here it is in Adj Vac Advance Can
If you get a chance, measure and plot the mechanical timing curves of your current setups. Then note the amount the vacuum adds and what vacuum moves it.
Even if you decide to experiment with it, you'll have a baseline.
It will be interesting to see if you've achieved a timing at idle that the engine likes with some vacuum advance or not.
