your theory is all dependent on the what the pressures are IN the engine bay at speed. it may be that your bay will have a higher pressure then the area where your 'intake ’ is…
The only way to make this system work 100% of the time is to make it a close system, so that the air coming into the air filer is ONLY coming from that duct… and you don’t need a scoop or any of that rice/grade 5 cool beans trash… a NACA duct or constant volume duct will work 100%++ better and NOT be a heat magnet in the process.
Just to clear some things up so IF your talking to someone educated in physics and/or rng. … aero does not reduce lift. and there is no such thing as down force… it’s called negative lift ( this relates back to the first correction )
With reference to this post, the two best ways to reduce drag on your car; make the front bumper as seamless as possible and don’t cut holes in your hood…