I guess it's the dilution thing that people talk about that I just don't understand or experience. Let me explain.
Let's say we use 55g per liter of water.
In a vac pot that means the 55 grams is brewing in less then a liter of water as there is always some water in the bottom. If the 55g is now being brewed with less then 1 liter, the brew in the top should be stronger because you are using less water to brew the fixed 55 gram amount. So, IMO, this stronger brew equals just right when it gets a little diluted after it travels south. To me, the end product tastes like, and, is brewed with 55 grams per liter of water.
And that is why I don't understand or experience the dilution thing with a vac pot.
My comment about using more coffee is just a preference, not to offset any dilution thing. I use the same ratios regardless of brew method, except for cross country driving,,,I'm real heavy on the coffee ratio then. :-)
Regarding when to add coffee....if I waited to all the water was north, bubbling, then added coffee, I would be cleaning a mess due to the bloom if using it at full potential.
Rich