Correct, a good placed to be is just below the "slot" for ported vacuum advance. This provides FULL MANIFOLD vacuum to the distributor with the slightest movement of the throttle. The factory was very specific with the location used for ported vacuum to the distributor and for good reason. We want full manifold vacuum in all light engine load scenarios to more effectively burn lean mixtures. Using a correct ported source the only difference then between using manifold vacuum to the advance and ported is that you will add timing coasting and at idle with manifold vacuum.
It's also best to have minimal transfer slot exposed, especially if you have opened up idle tubes, DCR's, etc for a larger cam and lower than "normal" vacuum at idle speed.
I'll add here that the transfer slot length and location varies considerably from carb to carb. Even so with most applications there will be some exposed at idle speed, which is a good thing as fuel flow is uninterrupted from idle thru transition to the main system.......Cliff
