Letters credit from Todd Klein via his Klein Letters blog (18 September 2016, http://kleinletters.com/Blog/ira-schnapp-in-worlds-finest-comics-part-1/).
This story states that the home dimensions of Mr. Mxyzptlk and Bat-Mite are not the same.
Letters from Jerrilee Vance, John Warner & Ben Lomand, Michael Liben, David Mendell, Vincent Krieg, Don Finley, Lewis Schrawyer, Jim Sammons, Thelma Brown, Ted Lawrence.