Cel/Toon shader not rendering correctly

I'm using the basic Toon Shader with an outline, and with the way it extrudes and re-draws vertices along the normal, it doesn't render correctly on my concave model. It seems like it needs to expand/scale the vertices, as well, which it isn't doing.

Is there another cel/toon shader out there that looks the same (and offers the same colorizing features) while rendering the outline correctly, too?