Either the windscreen must be so tall that its taller than your head when youre sitting on the bike so that you can hide behind it or it must be relatively low. Those quite high windscreens that only gives shelter halfway up your head and thus gives a huge airflow straight into your head are absolutely the worst. The original screen on my Tenere 660 for example was absolutely PITA. Fitted a 10 cm taller screen and its much better.
On the Tiger 955 I had I went lower than the original and also that was waay much better than original halftall...

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In the end everything will be fine. If its not fine its not the end....

I would hardly call them a trap - I find tall windscreens rather comforting, however I do not know how much of that comfort is psychological. Having it cover my entire body provides a sense of protection and safety, even if a superficial one.

That's exactly why I called them a trap. They provide a psychological sensation of being better and more comfortable, while not actually making the ride quieter. I guess they keep more of the bugs off your jacket...

Maybe I'm being obtuse here but my (subjective) experience has been that 'naked' bikes are wind noisy as hell and more tiring to ride - at any significant speed anyway. I can't say I've ever noticed how having my whole upper body directly in the airflow has led to a quiet ride compared to having some kind of barrier in front of me. OK, on some of my DIY attempts it's needed a bit of 'development' work to cut down on edge of the screen turbulence and in one case a 'blowing across a bottle top' whistle but these were easy to do.

The bikes with factory fitted fairings I've owned have all been pretty good and I can't say I've ever thought that they were noisy. My current GoldWing (an extreme example I admit) is so quiet behind the screen I can listen to the radio through the speakers at 70mph. Swapping from that onto a KLR doesn't feel like I've entered an oasis of calm.

And as for riding any distance in winter without some sort of screen - noisy or not - this picture, taken at the side of the autobahn returning from a long ago Elephant Rally, just about says it all. Temp at the time was around -10C :

Interesting direction we're going here!
I've ridden several bikes with BIG touring screens (talking about BIG Barn Door style screens now)

Ridden Gold Wings, big Moto Guzzi, to all sorts of BMW's; from old air heads, K bikes to latest RT's and GS's.

Most are fairly quiet and it can be nice sitting in a nice cocoon of still air on a cold day.

But ... In mostly WARM California and Mexico, where I ride, these cocoons of still air are not always a good thing. In the heat ... AIR FLOW is good.

The other big gripe we hear about wind screens is trying to ride off road whilst looking through a screen. I've done it plenty and hate it!

First did this on a friends R100GS in Baja. He had fallen, had a minor concussion. So I was conscripted to ride bike back to the highway, load into "sag wagon".

That GS was well set up, had good, fresh knobbies mounted, so it handled Baja's deep sand tracks fairly well (for a GS!) ... but I had a HELL OF A TIME riding as I was forced to look through that tall wind screen.

I could not concentrate well, affected vision, depth perception and mostly confidence. Not good. I only had to ride it for less than an hour, so I guess after a day or so I could have adapted. Overall, very un comfortable for me.

Later rode a friends XR650L through Mojave Desert. His bike had moderate screen but it really made vital terrain reading/line choice nearly impossible riding at a good pace. I hated it and crashed it. (minor)

Since then ridden a few other Dual sport bikes with screens off road ... I am NOT a fan.

The last point is the danger of having your throat cut it you bash into the edge of the screen in a fall neck first.
Unlikely, but somehow worries me.

So then the question becomes - why do all the rally-raid fairings are so tall? Can't be just to hide the nav tower? A big KTM Adventure is near-vertical where it meets the air...

no it's not that tall, it's about same height as on xt660z tenere
so you can still see over the screen freely when seated and when on rally you spend plenty of time standing up on pegs anyway, so screen won't matter. Basically it's for protecting the navigation tower from sand etc.

As mentioned, mostly to give a place to hang all the stupid crap those guys are required to carry.

At least some electronics are to prevent cheating, which is rampant in World Enduro and ISDE rally. Also to note, a few Dakar racers have been killed when they were squished through all that metal in the Nav tower in crash.

Having hard parts aimed right at your chest and stomach is something I would never do. I'd rather be lost.

The Dakar guys get up to very high speed, despite running just 450's. In the old days of 1000cc twins, when in Africa, speeds often topped 100 mph for long sections.

Nav towers were half the height they are now. So many riders died every year. They kept lowering engine size over and over. 1000 twin, 650 single, and now
450 single.

Now the tall Nav tower look has become "fashionable" I raced AMA Enduro 8 years, had two computers and a clock, no Nav tower or shield of any kind.
It's all just so stupid now. But KTM have sold this look to the public ... and it's pretty successful ... for now. Trends and fashion come and go. Most Americans have no idea what the Dakar is ... and could care less. KTM have built an entire industry on it.

it now costs over $100K USD to run the Dakar. So, a "rich kids" sport and really only KTM do a full factory effort. With about 70 guys riding KTM ... how can they lose?

Something with a big barn door fairing / screen and a pocket of still air where the rider sits can get to the point where it's a health hazard in really hot conditions. My two hottest days ever on bikes were both on GoldWings, although different models, one naked and one 'screened'. The feeling of riding the screened one in parts of Texas, around Phoenix and through the Mojave was, at its worst, close to being drunk. We had to stop in the Mojave as my wife thought she was going to faint. There's just no air flow at all - presumably what the designers intended.

The effect is a bit like driving a no air con car with the windows open but having to wear all your bike gear. Every other Wing we encountered had some kind of vent set into the screen that they could open when the temperature went up. Despite being able to buy them for $25 my UK brain couldn't see the point. Well I can see it now.

My rough 'how hot do I feel' calculations worked out that the fairing / screen was worth about 7-8C. When the mercury hits 40C in the shade and you're riding in the direct sun, that extra 7-8C you're feeling compared to the bloke on the (mostly) naked bike (riding with us) is a big deal. On the other hand up in Wyoming where it was 0.5C and sleeting that 7-8C bonus and (slightly) drier environment was very welcome. I got damp and chilled. He got soaked and frozen.

Right. Fixed the stock shorty screen to the FZ1S and did a few hundred KM over the weekend. Takeaway:

1) The road noise was maybe better - subjectively it felt that way, but it could be wishful thinking. Certainly was not worse. In that sense, yes, having your helmet in clean air is good for noise.

2) However, it was still not as good as standing up on the pegs. I guess the body of the bike spoils the air enough, and the engine noise drops off severely when you stand up, but standing on the pegs with the shorty screen gave the same effect as with the touring screen - FAR quieter than sitting down.

3) The downside of the shorty screen is the chest pressure; even in this heatwave, where coldness is not a concern (in fact I was wearing a mesh jacket), riding at any serious speed with the shorty screen meant leaning forward into the wind. Whereas with the touring barn door screen, I could sit comfortably upright even at speeds of... er, no, officer, I was not doing anything close to that.

4) Another downside is that with the shorty screen, the helmet's aerodynamics were suddenly important. I was using a Grex G9.1, essentially a rebadged Nolan N90, and at speed I could tell the difference between how it cut through the air and how my Shoei NXR did. Both straightline and, especially, doing shoulder checks at speed. The Grex was not terrible, but it was now A Concern, whereas with the touring screen, it wasn't.

5) What the shorty screen does give you, though, is exhilaration and sense of speed; and more maneuvering confidence. So for purely urban riding, I would actually stick to the shorty. But for extended trips, the barn door is going back on.

Yeah, I just test-rode a Gold Wing, played around with the electric windscreen. Made little difference. Had it up to about 170kph. 70mph - 115 kph - is not really the sort of touring speeds I'm talking about in Europe.