Thanks primorge, but I don't have the patience to read through walls of text on the off chance that I might find some pertinent information in there.

I did some experiments with a sphere and the same constant delta for each vertex in order to see what happens. It seems Poser uses different computations for the second and third coordinate depending on which octant the normal is in. Very strange! The best I've been able to do so far is to only use the component along the surface normal and ignore the other two. That produces very nice results, but it does not cover all the subd morphs one might want to make.

I'd say I give up at this point, but I know my brain won't let go of this, so I'll probably be coming back and trying more things.

-- I'm not mad at you, just Westphalian.