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Hi... I'm also a long-time follower of Vetter's progress on his last fairing. Although I'm new here, I hope you won't mind my sharing some observations as I studied your work (I'm working on a similar project, but not as extreme).
I think I figured out why your drop angle in the back seems too steep... On your blog I read the result for your calculation from widest line to the point of the vertical shape, "The imaginary point being a good 69 inches from the rear bulkhead where our tails ideal length is only 42.72 inches." I can see you are using the formula 1.78d and d=24" to get 42.72", so I assume you used d=39" for the vertical plane to get 69" to the point? But your actual d should be 2x the distance from the ground to the top of your head when projecting the ideal shape in the vertical plane, because the road surface becomes the centerline when working in the vertical plane. This means there should be a gentle curve from the back of your head to a point meeting the pavement over 10' behind you, and a very gentle drop in the tail vertically until it tapers to a point horizontally...
That said, I think the vertical plane is far less significant with a motorcycle than what is happening in the horizontal planes, and you are probably better off to plot horizontal planes at your waist, ribs, shoulders, and head; taper those to the proper point behind you, and then make one smooth shape that approximates all of that. Although compound curves are very difficult to manufacture, it seems to me that it is very important not to go straight into a 17 or even 11 degree angle because the air will separate right behind the seatback when it meets this angle and not re-attach easily.
Anyway, I'm looking forward to following this project, and hope I've been of some help...
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