Harley XR750 long-track fairing with custom large/shallow taper seat:
The HD and Norton JPN fairing are the main "classic" RR fairings that I know of that were wind tunnel tested instead of styled. The HD was done by the Wixom brothers in the CalTech tunnel and I think the Norton at MIRA.
A 13" wide seat like that on the red bike (shown is a 15" seat) added 500 RPM in top gear to a pretty stock CB125 Honda engined bike and was good with tuft testing at freeway speeds. That bike had about 7-8 hp. Most rider's butts are 15+" wide and the seat should match the rider and fill in behind the legs to give a smoother outer surface.
Here's a photo of the last version of my Laverda F750 racer with HD fairing and big seat (not the same as the "big butt" HD seat):
The back of the bike is more important than the front, and remember that the bodywork is there to streamline the rider NOT the bike. Unless you've got a CBX or a Boss Hoss the rider is the wide part of the combo.
Most rule books I've seen exempt the hands and forearms from the "rider must be visible from the side/top" rule.
If you look in this folder on my website
Index of /graphics/aero
you'll find a scan of an article (Free Speed) comparing 1970s RR fairings, including the Norton and HD.
Try to find a copy (used only available at this time) of John Bradley's "The Racing Motorcycle, Vol 1" as it has a lot of good info on RR streamlining including the wind tunnel runs on the Can Am LSR bike.
The trend in modern bikes seems to be to lower the top of the tank to make the rider's back more horizontal. Of course, that can make it difficult for the rider to see where they are going if they can't tilt their head back far enough.
cheers,
Michael