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That's not a good comparison. It works in the summer when you are ventilating heavily or have the coop wide open to keep the coop roughly the same temperature and humidity as the outside conditions, but in the winter as you start closing things up to conserve heat it becomes two separate environments. Relative humidity varies with air temperature. If you have two different air temperatures, the relative humidity comparison goes out the window.
As the temperature gets colder, you can cut back on ventilation to conserve heat. As temperatures drop you can keep cutting back on ventilation to maintain the temperature in the coop at a given level until the ventilation is insufficient to remove the moisture from the coop. At that point the relative humidity in the coop becomes the controlling factor and you need to maintain that level of ventilation at the expense of the heat.
The only way to increase the heat at that point is to add supplemental heat. Adding supplemental heat has several benefits. Obviously it will warm the birds, decreasing feed consumption, but it also "dries out" the air. As relative humidity is a measure of how saturated a volume of air is, and warmer air can hold more moisture, when you warm the air the relative humidity drops. By warming the air and lowering the relative humidity you can cut back on ventilation even further, while still maintaining temperature and humidity control, assuming there aren't other controlling factors like ammonia levels.