Hey Mike,
I can't say that I've noticed what you describe. I do understand what you mean: the inside of the "o" being a perfect oval, and the "swell" of the shade being to the outside of that oval. and vice-versa for the other.
The way I understand it, or at least the way it turns out when I'm practicing by tracing letters, is that the tip of the nib follows the perfect oval guideline, and is centered over it, so when the tines splay to form the shade, they do so equally to both sides of the perfect oval "guideline." The resulting shape is a perfect oval neither on the outside nor the inside; it's 'bulged' a little towards the outside *and* the inside where the shade is, from roughly the 7:00 position to the 11:00 position, the rest being hairline.
I hope I understood what you're getting at, and that this is of any help to you.