I think that food availabilty has as lot to due with their agression. I keep my four tangs (hippo, yellow, Red Sea Sailfin and Achilles) fed all the time. Either they are grazing or I'm putting a little something in. If I feed less frequently they certainly start getting agressive after a couple days. Wouldn't you? Remember traditional reef tanks were fed very little food so the fish were basically in a feast or famine situation so competition was high. Tangs are grazers and need a steady and stable diet to maintain.
FYI my tangs are in my 125 and will be moving into a 330 for X-mas.
Those four will also be joined by a powder brown and purple.