Some Elegance corals are small when we first get them, so they don't expand more than a couple of inches. Elegance corals that arrive in very good shape or ones that have been in captivity for an extended period of time can exceed 6 inches from the skeleton in all directions. Even straight up. I wouldn't call them aggressive. They normally don't bother mobile animals in the tank. Like any other coral, if they are placed to close to another coral or anemone, war can break out. Healthy Elegance corals do pack a serious sting, so they do need plenty of room around them.