Yes! My fish are over 3" and maybe getting closer to 4". I do think they are Acrossochelius paradoxus. Thank you! Hard to find much on them... I think they need a larger aquarium to swim in. Wonder if I get get the pet store to take them back. Not sure if they still want to school... they were not in a school that I remember... they act more like red tail black sharks and Baja sharks... but they are even quicker and even more active swimmers, darting around my plants with amazing speed and deftness... and they love feeding time they aggressively go for the frozen bloodworms, but so far haven't hurt any of my other fish.
This "acceptance" of the inappropriate situation may not last, in fact it is all but certain it will not last.
This seems to be a difficult concept for many especially newer aquarists to understand, namely that a shoaling species absolutely must be in a group. This is programmed into the genetic blueprint of the species, and we cannot change it. The behaviour of an individual fish in a shoaling species may seem to change, and this is because the fish must respond to this anomaly in some manner. Scientific evidence is clear that the normal response is aggression. This may show itself immediately, or days later, or weeks later, or even months depending upon the species and the individual fish. Fish introduced to a new environment such as bringing them home from the store tank where they have been for whatever number of days or weeks do not always follow the norm. But once the fish becomes more settled in its new home, things usually change. It is never a good idea to ignore what the fish considers essential to its survival--being in a group of its own.
Given the species, its size, its need, and you tank aspects, returning them would probably be the best course. One thing is certain, that keeping them in their present environment is not humane to the fish. We cannot fight against nature.