I've never really understood why these systems are not closed, ie: drawing air in from outside and expelling it through a sealed chimney type vent through the top of a case or visa versa. Surely it would make the cooling much more efficient. You wouldn't be adding warm air to the rest of the system or drawing warm air from the system to cool the rad.

as soon as you have a case with 3 top fans, it can go towards the front and get the cooler air in front of the MB, or for the single rad it can be mounted on the rear. one of the reasons i will add some thin balsa sheets to cover the rad partially towards other components (next build)..