im confused .. this seems to be contradicting the fact that many v-strom riders actually "raise" their shield and/or install a TALLER and sometimes wider shield to minimize the buffeting ..
anybody got some more input or explanation to the opposing theories ?
Sure, they're not really opposing at all. Mostly they're oversimplifications of the same impossibly complex fluid dynamics equasion.
When you put something in an air stream, in this case a windsheild, the air has to flow around it. For illustrative purposes, let's think in one dimension and imagine it as a rock in a stream.
Downstream of our windsheild rock, there's a teardrop or triangular area where the water is calm and makes a very slow swirl. In a stream it's called an eddy, in a windsheild usually a slipsteam.
The difference between the high/big sheild and low/no sheild theorys is in where they're putting your head, relative to that slipstream. Back to our rock, if it's a little bitty rock, there's only a small area of calm water. If you look at the water off to the side of the rock, there's still a strong current, but the current is smooth and steady. That's where your head would be in the low/no scenario.
If the rock is a big honking rock, there's a big honking calm area behind it. That's what the big sheild is trying to create, and where your head tries to be in a high/big scenario. The problem with acheiving that big calm area is that a motorcycle sheild isn't just a rock hovering in midair we can sit behind.
Imagine we've got our rock, be it big or small. Now, imagine we plunk something, say another rock or a knee or a motorcycle mirror, in the water right near our rock. Now there's two slipsteams, but they're interfering with each other. A simpler way to think about it is that every extra thing we put in the stream near our windsheild rock is changing the way the stream around the rock behaves, not always in a desirable or easily predictable way.
The result is that if someone doesn't mind the steady solid stream of air, they'll be pretty happy with the low/no route, as it's much much easer to keep the air clean, since their head's not near anything that can cause weirdness. If they want calm air, rather than steady air, they need to go the big/high route, but because of all the motorcycle and person interfering with the air stream, it takes some work to get the air clean.
There's other partial solutions, but I've already written a book, so there's the basic idea.