: I just know that you are correct. I just can't figure out why Nick
: insists that I have it correct in the figure.

When you fitted the first form onto the end stem, did you remove material equivalent to the thickness of the end stem? How does the bottom of the form match the shape of the bevelled internal stem now that you have removed material to fit it correctly?

It is possible that Nick was concentrating on the way the bottom of the first form met the internal stem. In your photos, it looks to me as if it matches. That gives the impression that you have fitted things correctly. Unless of course you failed to remove the thickness of the end stem from the middle of the form, in which case the combined effect of two mistakes makes it look as there is no mistake.