You actually answer your own question here somewhat.
First for the record if you follow my postings on ignition you will find that I often suggest using a hand vacuum pump to tune your vacuum advance. You really cannot beat the utility of a vacuum pump to tell you when (what vacuum level) your vacuum advance starts to move and when it is all in (again in terms of vacuum level). Doing the actual measurements is even better than using the manufacturers specification of a range. If you measure it you know what you have without any ambiguity or manufacturing tolerances.
AR35. Looks like it starts at 2-4 and is pegged 6-9
Very similar to mine, mine starts at 3" and is all in at 9" and provided 20*.
Steve, why would one not chose a vac can that fully deploys at say 1-3" of vacuum vs. getting one that deploat at 2" BELOW your lowest vacuum?
For the record, my GM can deploys at 1-3", and adds 20*, but I trimmed it back to 14*.
I believe you later elaborate that 1-3" is only the start and not full advance. I have not heard what your idle vacuum is but starting to deploy at a rather low vacuum would be appropriate with an engine combination that idled with low vacuum.
But that aside, this is a very
common situation, needing to trim or reduce the amount of vacuum advance provided. Many of the vacuum cans provide too much advance and need to be limited to a lesser value.
Note also that your later response says that you really have full advance at 6-9". This would be appropriate for an engine combination that idles at 8-11" of vacuum.