That 1 sq ft per bird is a rule of thumb often used on here for ventilation requirements. I don't know of any scientific justification fort that number but we need something when people ask and it should work most of the time.
Thanks for mentioning you are in Kentucky. If you modify your profile to show that it will always be available. That can help out in a lot of different ways. Your winters can be pretty cold but not brutal. Your summers can be pretty hot and humid.
Whether summer or winter, you want a small amount of ventilation up high (over the chickens' heads when they are on the roost) to handle any ammonia that might develop from the poop. Ammonia is lighter than air and it doesn't take much of an opening for it to escape. You don't read about ammonia on here much because even a small opening up high handles ammonia. Managing the poop helps also.
In summer, you want ventilation to get rid of heat. Hot air rises but only if there is cooler air to replace it. Gravity is the driving force. The greater difference in the temperature the more air can be moved. There are a lot of different ways to provide venting up high. They can all work though some may be more efficient than others. If the wind is blowing, openings so you get cross breezes can move a lot of air but even if it is dead calm the differences in air temperature will also work. I like to bring air in down low from a cooler spot. That may be shade if your coop is shaded but in Kentucky the coolest spots are likely to the north or east of your coop. The south and west sides get the hotter sun.
In winter, you have different issues. You want to remove moisture from the air. When temperatures are below freezing, high moisture can lead to frostbite of the comb and wattles. Moist air is lighter than dry air so again you want openings up high. But you also do not want a breeze strong enough to ruffle the feathers to hit them. They stay warm by trapping tiny bits of air in their down, these tiny pockets of air insulate them, just like a down coat can keep you warm in winter. But if a breeze lets those tiny pockets of air escape the down loses its insulating effect.
Air flow in your coop affects that. There are some designs (like the Woods coop) where you can have one wall pretty much open and breezes still do not get back to where the roosts are. But that is a specialty design for colder climates. The way I managed winter ventilation when I was in Arkansas (similar conditions to Kentucky) was to close off my low summer ventilation but I had permanent openings up high on all four sides to get tremendous ventilation up high.
I personally do not see the relevance of a sq ft per chicken number. The only thing I can see where that might have an effect is the moisture produced in winter by an individual chicken's breathing releasing some moisture in the air and the moisture that evaporates from its poop. The heat from the sun on the building in summer or the moisture from sources other than individual chickens like waterers or rain are not individual chicken dependent. Still, you need something to go by and it is as good as any other rule of thumb I can come up with.
Hens go broody when you don’t want them to… and won’t go broody when you do. 
