As long as the electric fan doesn't deflect the normal airflow, go ahead and leave it on there. I'd suggest shimming it forward an inch or two just to be sure the blades won't act like an air deflector.
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!