At speed there is often a high-pressure air bubble at the base of the windshield. That is the basis of Nascar intakes and the typical open rear Vette type scoops. If the scoop shown here has benefitted from rear holes being added, it might be from the additional air from the rear and it's slowing down front entering air, which could mean less turbulent air also at a combined higher pressure. We also do not know for certain if the front air scoop entrance is below the boundary air separation or maybe only partly above it, which impacts the positive contribution of any possible rear entry air.