Right behind the fan motor, there can be no airflow because the motor is there, blocking it. The center of the radiator gets no airflow. Spacing the radiator off the fan anywhere from a half inch to a bit over an inch will tremendously help. However, because air will be filling the general space, it is better to then have a duct to make sure that all air from the fan(s) goes through the radiator. In my case, I am using a shroud to put 4 80mm fans through a big momma. Here's what it looks like thus far (the final one will be outa sheet metal).
[ 10-09-2001: Message edited by: Kevin ]