The later illustration shows the duct buried in the hood. To preserve the driver's sight-lines?
It definitely starts in the stagnation area — I have no idea what happens when you 'cross the streams'.
edit:
Presaging teoman: Oh look — first post [welcome]
I'm imagining a 1950 Ford, with the radiator tilted back (electric fan in front), a duct on the underside of the hood (lots of headroom with a flathead V-8) and louvers all over the back half of the hood.
Satin black with red wheels.