Good question, and I agree the charts are only a starting point — behavior and how much time the birds spend confined matter a lot. For standard-size hens, a practical rule I use is about 3.5-4 sq ft of indoor coop space per hen, plus about 10 sq ft of run space per hen.
So for 6 hens, that works out to roughly 21-24 sq ft of coop (for example, a 4 x 6 ft coop) and about 60 sq ft of run (for example, 6 x 10 ft). For nesting, allow about 1 nesting box per 3-4 hens, so 2 boxes would suit 6 hens. For feed, plan on roughly 1/4 lb of layer feed per hen per day, so about 1.5 lb per day for 6 hens, plus fresh water and free-choice grit/oyster shell.
If the birds are locked in all day with no run or free ranging, I would go bigger than those minimums, and make sure ventilation stays good without drafts directly on the roosts. If they free-range most of the day, the coop mainly needs to be dry, draft-free at roost height, and comfortable for sleeping and laying.
