Cichlids are much more complicated in pair selection than many other less evolved species, and do not only communicate by sight, but with tail beating, that helps determine each others strength and pair bonding thru the movement of water, and other methods that may include sound and scent. With a plexiglass divider, some of these methods are not often possible.
This is one reason why egg crate though unsightly, can be very successful in pair formation, as it allows the movement of sound, pheromones, and the water movement/pressure to pass back and forth.
It even allows for spawning thru the divider, preventing one of a pair from killing each other.
I have had pairs that would normally kill each other, spawn this way.
Male fertilizing
female putting down eggs on the opposite side