Roof spoiler effectiveness

[trevorbrady]

This is just a thought but if the problem is with air gathering under the wings (fenders) and causing lift, then could wheel arch liners not be used like in modern cars that would have the effect of minimising the volume of the fenders and therefore reducing lift? Keep the liner as close to the wheel as possible to ensure the smallest volume of trapped air. Especially if you wanted to keep the car looking stock from the outside (i.e. no holes in the fenders)