Here's what McIntosh says about the 16ga Super Fox (p. 216 in his Fox book):

"In "Modern Shotguns and Loads", published in 1929, Captain Askins reports that Fox attempted to create a 16 gauge Super as well but failed. "The reason," he says, "was always a mystery to me, and I was there trying out chamber, bore, choke and cone changes until I got tired, never being able to produce an average pattern of 80% with factory cartridges."