I have many tangs in a 6' tank but I don't entirely agree with the notorious tang police when it comes to tank size
. I have never seen my fish do full 6' laps of my tank but they do have plenty of room to roam around or to find privacy.
I would personally rather see someone properly care for and nurture a tang in a small tank than see someone neglect one in a big tank. Pick a smaller sized tang like a Kole or Yellow and keep them happy, that's what matters.