Goes to show you that superficial data can be quite contradictory, which gave rise to the saying "Every tank differs".
Details matter in understanding why sometimes things go one way, while going the other way other times. Sometimes ichthyo-forensic troubleshooting and analysis is needed.
There must be a logical reason for this contradiction.
If not ID'ed, every tank differs
If kept in a smallish tank, it is quite understandable and expected that the fish that have just sexually matured would squabble in the same smallish space. Mine was 4500 gal. They could easily get out of each other's faces.
As to when small, mine were in a 55 gal. If they were small in a 500 gal, I think they'd be fine.
Details matter.