Providing a strong blast of current at one end of the tank helped me out big time when I had my two regals. Like most fish-tangs love to swim, to search for food(grazing) and also for exercise. Reducing swim space by placing most fish in a
tank like Brad said is #!?*@# in my opinion, yet we all do it.
I would suggest like mentioned above, create a full run from side to side or better yet a full oval around the entire reef like naesco said. Then position powerheads or returns to make a decent flow in this area.
When I had both my regals before they outgrew the tank, this worked great for 2 years. I made a figure eight pattern with my rockwork, then re-adjusted the powerheads to blow in the same pattern. After only two weeks the tangs would start swimming around in opposite direction of the current. I noticed they would do this almost right after they finshed eating, as to burn more energy so they would have room for some more food
I plan on getting another baby blue tang one day, as I have found it a larger home after it outgrows my reef in a year or two. But that means I would have to rearrange the rockwork and sell off corals, so maybe I will wait until my 8 footer is up and running-which will be some time yet
cheers, Rich