OK, not to seem to be ignoring this thread, but my research is so far unverified. It has always been my understanding that there is an extra lens or prism involved with the image path on a straight vs angled spotter, with the angled one having the extra surface.
It is also my understanding that Ted is also right to a degree as changing the light path geometry is possible with a prism position change. It has been my understanding that this is maybe not so simple as a flip of the prism mount, but if done will still require another glass surface somewhere.
I just got off the phone with Vortex and the guys I talked to said they "thought" there was another surface in the angled.
I have a couple of other questions waiting answers out there and am just waiting. This question is sort of like a little mosquito buzzing around just behind your ear.
So anyway, when I know, I'll either admit the error or ... It seems you can learn something any time you hit the submit post button.
Probaly should PM Ilya