Helene, your observations and presumptions are much alike those Martin Hallmann and I made and are presented in our new book on Paro’s which has just appeared in print.
The main point is: Keeping Paro’s pair by pair in small aquaria is biologically “wrong” but nevertheless the best method to receive a good number of offspring. The “right” method would be to keep small groups of them (one species only, of course) maybe associated with some red Betta spec. and some friendly Boraras spec. in bigger tanks (at least 60 or 100 liters), but you cannot handle them appropriately in that milieu as feeding and rearing of the young are concerned.
But if you did (or do) you will see that they are not monogamous, that one female will visit neighbourung males, and one male will invite several females to its cave. The living in small groups seems to be much more appropriate for their scheme of behaviour than that in fixed pairs, but ….
we are mostly occupied by getting them fed and spawn and breed which is to be mastered in a rational way in pairs in small tanks only.
So, you rightly infer that they do better in small groups if the space is sufficient. at least during that long period of adolescence, but, in principle later, too. Their highly endangered status forces us to make breeding a very important aim (we lost all Paros that were imported in the 20th century already after ten years at the latest, mostly after one year already). Keeping such fish in aquaria presupposes that we accept to look for breeding and sustainment in the first rate, but sometimes we experience that this entails structural limits of the aquarium.
Nevertheless, you are right, not as a principle guideline for keeping Paros generally, but as an insight for the best milieu and adequate behaviour. Maybe, from time to time – when you have propagated them before to a safe number – you can follow your insights and experience what is certainly closer to their natural way of living.