No, compound curves...the shape of the shield. Compare the OEM shield to aftermarket models. The multiple curves and rear trail are what give the OEM its biggest advantage, still quiet air right back to the passenger.
If I desired I could smoke a cigarette at 180km/h, but I'm not a smoker

Most aftermarkets are just big and simple shields and stand up too abruptly, Venarious' shield is a good example of that. His might be adjustable to tilt back a bit, but the simple shape probably wouldn't help much anyway.
You can see some of the curve on my windshield in this picture, on its left side over the building behind it. When viewed from the side its shape is more dramatic. You can tell in an instant that time and effort (in a wind tunnel) went into the design of that shield. Peolple on the Valkyrie forums are told the same thing by 80% of the respondants when they ask the same question about what shield to buy. It was standard equipment on the Valkyrie Tourer.

There is no such thing as a bad motorcycle.
Honda XR650L Dual-Sport