[aerohead]

Since the sub- Cd 0.17, M-B Vision EQXX has non-ventilated wheel covers, and low drag was of paramount concern to M-B, it implies that, like so many other 'record' vehicles: when you want really low drag, get as close as you can to MOON wheel covers.
One wind tunnel investigation by John Shinella of GM, specifically tested tape on the wheel covers of the 1982 Pontiac Firebird Trans Am. It registered the lowest drag of any configuration examined.
Renault, for their sub- Cd 0.19, 1987, Vesta-II concept, essentially 'taped' all but one opening in their wheel covers. It obviously took care of brake cooling, plus allowed for the valve stem access. Also, the actual opening on these covers were uni-directional in design. Something of interest to us.