I am not in anyway discounting what you said. Hopefully adding to it. Certain fish Chromis, Damsels, live in large shoals on the reef, shoals not schools, there is constant bickering and the loser has miles of reef to get away from the aggressor. In almost any tank size1- 7',8',10' there is not enough room or usually rock work/corals to evade so 1 gets singled out until dead from damage or stress. That keeps happening until you are left with 1. Add to that you can only keep so many in a given space and its harder to spread the aggression. Same goes for most fish, If you can actually get a schooling fish they are a little less apt to really tear into each other, but squabbles and lack of space still happen. Now add these typically solitary fish that choose a section of the reef to call home in the wild that might be 10-20' of space and they defend it from anyone trying to get in for shelter or food. They will chase the intruder through the reef out past their imagined border. Where is that in a 2' long tank? Sometimes the stress of living in close proximity keeps them more "subdued" but they are not living their best life.
