Baffles definately work.  Full scale break the rules of thumb many have stated here because of the baffling.  If you keep the air close to the engine you do not need as much air.  That is because with no baffling, much of the air going past has little to no cooling effect.  I would think 1" would be marginally enough with good baffling.  Might want to baffler air from the other two holes toward the engine for good measure.