My understanding(as a guy on the internet who eats pizza for breakfast) has always been that without a leading gurney flap on a hood vent, it is not going to extract efficiently. The air pressure under hood has to be greater than the air pressure on top(kinda sorta). If you look at the verus hood vents or the driveway labs, they have a gurney on the front to trip up the airflow and create a little low pressure zone. I have the driveway labs vent, and in the rain it actually causes the water to swirl inward on the windshield.
https://drivewaylabs.com/collections...ood-duct-large
https://www.verus-engineering.com/sh...ory=41#attr=64