Is true that the gap moves around with the vacuum. That happens because the diff ratius built into the distributor.

The reluctor is perfectly centered, so the circle gets the ratio from center.

The pickup coil is on a baseplate with different center than reluctor, so the ratio draws diff

is simply and basic geometry

If you adjust incorrectly the gap, you can even BITE the reluctor when vacuum is working, depending on how much advance you apply.

THE ONLY SOLUTION IS... play with the pickup coil position, bending the bracket here and there untill get the SMALLER VARIATION AS POSIBLE.

I made it, and got .009 with vacuum off and 0.007 with vacuum activated. That was way before I adjusted the vacuum action with the 3/32" Hex key, what it was really big.

Now I shortened the vacuum action travel, I guess I must be in .009" off and .008 on, or MAYBE still the same .009