[durkie]

my understanding is what you're talking about only applies for traditional conduction/convection, where you're expecting moving air/water/... to act as a heat-transfer medium, so you want to maximize your surface area of your radiator and fluid flow rates to facilitate that transfer.

what they're doing here is shifting the transmission characteristics of radiation to be within the infrared window (https://en.wikipedia.org/wiki/Infrared_window) so that it's kind of like surrounding air (and water vapor, most importantly) aren't present at all and you're radiating in to the giant cold heatsink that is space.