All of my maroons establish a territory of about 1 cubic foot. They let selected tankmates in that area and others are run out of that area.

A 30 by 30 inch cube might support a mandarin if you really provide a lot of pod growing stucture and have a good culture going in that tank. It will help to feed the pods as well as keep a slight trace of iodine in the system via either an additive or frequent water changes.