vtec-e , I think your covers look
fantastic ( once painted. )
It just looks ...'right'.
I would suspect that your method is indeed a better way to reduce the frontal area of a wheel skirt, yet have attached flow to the back of the car.
You have a really tight fit all around, and I would think that air will slide right past the wheel without any real turbulence. ( Especially if the wheels are smooth ).
Disclaimer : I have no clue what I am talking about. What I said is pure guessing.
To test this though ( and prove me wrong
) it would really be interesting to see a tuft test around this area of the car ( hey - while you're at it you might as well tuft the whole thing. It's really quite interesting to see how air travels around your car ! )