Ram Air-vs-Cowl Induction.
Ducting from the base of the windshield is NOT ram-air. There are distinct design differences in the way the air is pressurized, hence different names.
Ram Air utilizes a forward-facing scoop or duct that relies on air coming in at relatively high speeds, to hit a diffuser and turn to pressure. These systems are very complex to properly design. This stems from the fact that the velocities required are very high, due to the relatively small opening available, and size of the diffuser that can be fit under the hood.
With the cowl induction, though, your velocity at highway speed is enough to get the benefits of a good ram-air at 100 to 120mph!
This is due to your CAR being used as the intake, and the windshield being used as the diffuser. What happens is the same as inside the intake duct in a ram-air system, the dbig difference is that it occurs externally to the intake system, and utilizes wasted energy---any car can utilize this--unless it's fery aerodynamically slippery. A Honda Insight probably doesn't have a lot of damming effect at the base of the windshield, nor a Lambo Diablo or Countach.
Many things can be done to up the air available for the cowl induction. Strakes on the fenders helps raise the pressure, and the more upright the windshield, the more pressure you get. Small, but tall strakes at the A-Pillars keep the spill-off from occurring and are just as good as fender strakes, but hurt top speed (at speeds over 150, they can actually flatten or fold over if not properly reinforced with beading!) Fender strakes help with directional stability at higher speeds, as well as placing them on the roof.
Again, I digress. Most of the performance improvement from cracking your hood is because it lets hot underhood air OUT and lets cooler air circulate underneath. Cooling the ambient temperature of the engine operating environment is good, specifically, that the 340 air intake for the stock box will probably have 15-40 degree lower intake air temperatures from simply cracking the hood and letting the hot air OUT! I've seen high-capacity 12V pancake fans under the battery and mastervac to pump out hot underhood air in stop-and-go. Louvering the hood near the rear, even louvering the battery and washer covers helps a bit--while the car is in forward motion.!