I have a 250 gallon and my puffer that is 10 inches does that about 3 times a week for about 3 hours, my stc does that everynight constantly. I dont really think it is tank size. It may be the fish are not happy. I heard fish in a round tank do that all the time. It may be psychosis. Seriously, something is not making them happy and they can injur themselves doing it by constantly rubbing. It may be a nervous twitch thing. I have fish that will not leave the bubble wand. I try to provide everything possible to make their stay as comfortable as possible but you cant please all the fish all the time. Just my thoughts.
