my limited YT understanding is that it supposedly blocks the air more inline with where the legs are (which is going to block air anyway)-Indoor track bikes are big into this design- but perhaps even more marginally importantly, having a tight clearance between the tire and the forks creates more vortices and drag than having a lot of space to reduce pressure. This makes a bit of sense for me near the fork crown, where the top of the tire and spokes are pushing air (frontwards?) as it spins, and the forks themselves are pushing air (rearwards) into the same tight area as the bike moves forward.
This was from watching some Dylan Johnson gravel video where his suspension gravel fork was more aero than his stock gravel fork (in a wind tunnel). The suspension fork looked very un- aero, but has wide space for air to flow through, so it reduced wattage. He and the wind tunnel guy were surprised by the results, but that's what they concluded.
I'm going to go put on my aero socks now and go ride 