I believe the one inche per five gallons is a good rule of thumb, to use in newer tanks. But, this is merely a guide to start with, but one inche per 3 gallons is more realistic, once things get going, in many tanks. 1 inch per 2 gallns, really never should be exceeded(and this is in an established tank, where the biofilter can handle the load..The real indicator though is, water quality. However, if the tank is young, then it is hard to go by. This is why we have to set limits ourselves.
Your tank, is nothing like the ocean, which can handle the bioload much better. It's filters actually have much less inches per gallon. maybe one inch per 50,000,000 gallons is more like it.
Alos, swim area is another reason. On the reefs, there is room to swim about, even though they are schooled. The whole school moves, but they are able to move.