The most popular model for a field emission diode has been a spherical cathode inside a concentric spherical anode. A much more accurate model assumes the cathode is an equipotential of a sphere centered on the tip of a narrow cone. The authors have discussed this latter model in some detail. The purpose of this paper is to point out similarities between the sphere and the sphere-on-cone models and to correct errors in our previous paper. The similarities discussed here make earlier results more useful in concept and practice. In particular, the sphere-on-cone model predicts a source size from 1.5 to 2.6 times larger than predicted by the simple sphere model that is normally used.