Visual boundaries are just that, visual features the fish use to separate their individual territories. Typically, if they can see each other they will display at these boundaries and not cross them. If they cross, then it isn't a boundary. You need to build areas where less dominant fish can hide and still have their own territory. I always suggest that each female have a territory of 1' / 30cm in diameter. BTW females are much more territorial to other females than males. Males of polygamous species like A. cacatuoides will consider the whole 2' tank as their territory. When a female has eggs/fry the male will he be unwelcome in her brood territory. Once the fry become freeswimming females try to expand their territory as the brood grows. If both females have broods at the same time deadly fights can break out where the male and less aggressive female can be killed if they can't or are unwilling to hide. I did have 3 females successfully breed and raise fry in a 2' tank once. The middle 20" / 50cm of the aquarium was choked with a mass of Java Moss that filled the tank from top to bottom and front to back. It was hard for the fish to ever see each other.
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