Are you familiar, by any chance, with general guidelines (see below) and/or just trying to collect as many personal opinions as you can?
http://injaf.org/articles-guides/understanding-fish-stocking-guides/
http://www.planetcatfish.com/forum/viewtopic.php?f=2&t=37977&hilit=+thumb
There is much confusion about this common name. If we are talking Hemibagrus wyckioides http://www.planetcatfish.com/common/species.php?species_id=19 with a maximum full length of about 3.5' then IMHO the minimum footprint should be 3.5 times 4 by 3.5 times 2. The vertical dimension should be at least 1 times the fish's length but more is better.