My mistake was not adjusting the Diffuse Glancing Level value to compensate for the reduced affected area. When I set the Minimum Glancing Angle to about 75, the shading distortion disappeared (along with my ink line). Setting the Diffuse Glancing Level to -5000% restored a black edge to the object--and this time it was crisp enough to stand on its own, without Cel Shading. Reducing the Minimum Glancing Angle produced a thicker line; increasing the Minimum Glancing Angle resulted in a thinner line.
While I could have used this type of Fast Fresnel inking after Super Cel Shader, I still wanted control over my ink colors. So I applied Fast Fresnel first, then Super Cel Shader.
Here's another take on the elf-girl, with "colored" inks:
RGB 128 128 255
Fast Fresnel--Minimum Glancing Angle set to 70 degrees; Diffuse set to -5000.0%
Super Cel Shader:
Zone 1 0.0/0.1 Paint Brightness 1.6 (main "ink")
Zone 2 0.1/0.65 Paint Brightness 1.5 ("shadow" paint)
Zone 3 0.65/0.7 Paint Brightness 1.6 (puts an ink-like line between the highlight and the shadow)
Zone 4 0.7/inf Paint Brightness 255 ("real" hair color)
RGB 255 204 187
Fast Fresnel--Minimum Glancing Angle set to 74 degrees; Diffuse set to -5000.0%
Super Cel Shader:
Zone 1 0.0/0.1 Paint Brightness 1.0 (main "ink")
Zone 2 0.1/0.7 Paint Brightness 1.2 ("shadow" paint)
Zone 3 0.7/0.73 Paint Brightness 1.3 (puts an ink-like line between the highlight and the shadow)
Zone 4 0.73/inf Paint Brightness 1.5 ("real" color)
RGB 128 1 255
Fast Fresnel--Minimum Glancing Angle set to 0 degrees (for curved highlights); Diffuse set to -50.0%
Super Cel Shader:
Zone 1 0.0/0.1 Paint Brightness 0.5 (main "ink")
Zone 2 0.1/0.5 Paint Brightness 0.7 (shadow paint)
Zone 3 0.5/0.9 Paint Brightness 1.0 (real color)
Zone 4 0.9/inf Paint Brightness 255 (white "highlights")
You may be wondering about the Zone 3 settings on the Hair and Skin. Well, I have a theory. On real hand-painted animation cels, you'll see a thin band of slightly-darker color between the shadows and highlights. It's paint applied to the top of the cel, defining the highlight and shadow zones before the rest of the color is filled in on the back. The Zone 3 settings are an attempt to mimic the look of that "definition" ink. It's a subtle effect that might help to make the illusion of Cel Shading that much more convincing to your audience (emphasis on "might"--I honestly don't know if it would work. I do like the way it looks here, though).
Here's the hair with a thicker "definition" ink set to a lower Paint Brightness:
Inks like this sacrifice a Color Zone, though. If you want colored inks and definition inks, that leaves you with two actual paints per surface. This is more colors per surface than most televised cartoons, true...heck, it's probably more than most anime (sometimes I think the #1 characteristic of anime is the art of getting the maximum impact with a minimum budget--even the spectacular Ghost in the Shell featured several scenes with next to no "animation"...but I digress).
If you want more than two colors, you'll have to drop one of your "inking" Zones. Either lose the colored inks (by applying a -5000% Diffuse Fast Fresnel after Super Cel Shader, you can put a crisp, black "ink" line around the edges of your surface, on top of the Super Cel Shader "paints." No choice of color, though--well, you can use a 5000% Luminosity Fast Fresnel instead of a Diffuse Fast Fresnel, for a white line), or lose the "definition" inks.
If you're wondering why I didn't use a single color for the Skin "inks"...here's why:
I see potential for mimicking certain anime FX here..."metallic" FX, for instance. Or that crystal chick in Galaxy Express 999 . But I don't think I've seen hand-drawn anime like this. Hand-drawn comics, yeah, but not hand-drawn anime.
Hmm...maybe I'm looking at this wrong. I'll set all the "inking" Zones to Paint Brightness 0.0 (and shade her clothes in a similar fashion)...
Turning on Cel-Look Edges could help...
...but I like this one better. :-)
The settings for these surfaces are almost exactly the same as the ones listed at the top of this page. Only difference is that the Skin and Hair are set to 100% Glow.