Since you started off with so many disclaimers, you already realize that the question isn't really the right one to be asking.
Let me
answer it not as a gardener, but as a forager. Most of the time I forage for food I do it from inside my
fence lines (my garden), but I'm not adverse to gathering a harvest from elsewhere, when the occasion arises. I grow no kudzu of my own, but I know of plenty of places around town where I can stop and fill up a bag's worth. I have a loquat tree that is too young to be producing, but the two big ones at the library down the street usually have a bounty in the springtime that goes unharvested. I can forage there, bring home a harvest, and that's less "garden space per person" out of my
yard.
And then there is the matter of trading. My neighbor has a bunch of pecan
trees and always has a supply of pecans on hand. However, he doesn't grow any turnips, which I do, and he is always willing to swap pecans for turnips. How does that affect the calculation of "garden space per person"?
I think the "garden space per person" question comes from a factory mindset, thinking that for a certain size factory, we get a certain amount of output. How about we alter the question more along the lines of what a field biologist would ask, "how much foraging territory per person?" That's a question that is easier to measure, and it works for both carnivores and herbivores. Tigers have a huge territory, something like 25 square miles, because they have to range over quite a large distance to find a nice size animal to take down for a meal. Even if you ask "how much space does a hunter gatherer tribe need", it depends greatly on the productivity of the ecosystem. Plains Indians covered vast distances as they followed the herds of buffalo, but tribes in California were much more sedentary, especially along the coast, where there was always something to eat in the
local tide pools.
Foraging is also more in keeping with the idea of a forest garden. My property is not a forest garden yet, maybe on its way to being there, but I look upon my garden not as a factory where I can collect harvests and more as a place where I have optimized the foraging so that I can always find something to cut and take into the kitchen when I'm hungry. Some crops you really do have to do a formal harvest and then prepare them for long term storage (corn, peas, peanuts, sweet potatoes, etc.), but there are many others that are ready to be harvested any time you are (onions, hot peppers, leafy greens, taro, herbs, etc.)
If you are in a climate with a year-round (or close to) growing season, you can come close to that continual harvest, and then the amount of garden space required to support a person begins to approach the biomass productivity of the
land. If you are on a tropical Pacific island and live on a diet of taro, coconuts, and bananas, you probably don't need much garden space at all and an acre of land could support 10 to 20 people. But humans like variety in their diet, and even if they could get all their requirement from a small plot of land, they are much more likely to think of the whole island as their foraging territory and they will know what's in season and when and where to find it.