The best thing you can do for the efficiency of any type of fan is to build a properly shaped shroud around it. Position the back of the shroud so it's halfway back on the fan blade, even with the spider the blades mount to. If the shroud opening is either ahead or behind that point, the airflow will be reduced. The shroud assures that ALL the air the fan moves will pass through the radiator.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!