I would invite others to make a hood splitter like I did and check your mileage. Imagine your vehicle from the top down rather than just from the side. My design was not intended to cover the wipers. Using coroplast is a very crude way of testing. I am going to make one that blends into the hood next.
Here is my trike at speed, it has the same canopy as my varna.
Ever stick your fingers out the window and feel the air flow at the surface of the roof line your car. At the windshield the air is strong right at the surface. As you drift your fingers back a foot or two back from the windshield top; you can feel the major flow move outward a couple of inches. Anything we do to help keep the flow attached is going to make the car go through the air better.
If you want to prove this wrong then start recording your mileage and doing your own testing.