I have an opinion, and its predictably not shared by many I would guess. A shrouds main purpose is to provide a venturi for a rotary fan to improve its pumping effiency. The closer the venturi tube, the better, of course in a car in can never touch. The next purpose is to channel the inlet air thru the item being cooled, the radiator. Many think that the entire amount of air the fan is moving must be moved thru the entire radiator. This is where I disagree. I believe only enough air needs to be drawn thru the radiator to provide enough engine cooling under the worst conditions, ie high ambient temps, no car movement, without too much temp rise before car is likely to move, that's a time factor, and every car/situation is different of course. The problem I see with over shrouding, which I think is the point of your question, is at speeds over say 60mph?, your fan becomes pretty much an obstruction to air flow and is almost useless and a hindrance. If the restricted air can find a new less restrictive path around the fan, but still thru the radiator, you have a good compromise solution. Others may differ.
https://board.moparts.org/ubbthreads/show...e=1#Post7973457Pic #43 shows a simplistic workable solution
