Best gap between fan & radiator?

Evening folks,
I plan to make a fan shroud, but before I tackle this project I wonder if there is a "best gap" between the fan and the radiator. Presently, I have about 1.75" there. There is a 1" spacer between the water pump and the fan. Could that come out? Is there a need for that spacer? The gap between the fan and the PS belt is just over 2". There has to be enough room for a thermal clutch, but darned if it isn't tight in there already to put this fan on/off.
Thanks,
C