Let me say it differently. The longer the water is not in the heated engine, the cooler it would be going back in. Yes, air movement and radiator size is also a factor. Fast moving coolant would not be as cool as a slower moved coolant. Now, there is a limit on how slow or fast the movement is. Think, as in an AC in a car. A low-speed fan would make the air colder coming out of the vents, then it being on a high speed. Yes, you would have more air movement but not as cold.