just because a fish has miles and miles of swimming room doesnt mean they will use it. Most fish stick to a small area to graze and protect.
I disagree with this statement. When diving in Hawaii I followed some various tangs around, and beleive me they cover a good amount of territory in the wild. Especially the bigger tangs like unicorns, and naso's. The yellows covered their share of territory as well.
I have a small 2-3" yellow tang. When I originally put him into my 55 he constantly darted back and forth across the tank, and in/out of the LR. I though he was happy, until I moved him into my 240. I noticed a big difference in his personality. He no longer darts back and forth, but takes his time,grazes on the LR, and slowly moves throught the entire tank.