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.