You want to space the fan so half of it is inside the shroud, and half is (outside) behind the shroud for best airflow, so the fan works with the shroud to act like a funnel...
When they design the cooling system, they use an acronym for that called FOOS (Fan Out Of Shroud).. By changing the overlap they can tweak the effect of the fan to pull the air directly THROUGH the radiator and condenser for maximum cooling.... You start at 50% overlap and move it until you find the optimum overlap for the combination...