I have a recent pair of crosshatches in my 120 currently (hopefully SOON going into a 220). My pair is small (male 5-6", and female approx 4"), but the male is near constantly swimming. Luckily, I have very little rock, and what rock I have, is in a very open structure, so there is plenty of room to swim. I keep my SPS trimmed way down, so the top 1/2 to 2/3 of the tank is open water. I also have very few busy tank occupant. The largest are a square anthias and a juvenile chevron tang, but they are more reef and rock fish, although they freely come to the open with the triggers. A word of advice- it took all of about 2 days for the male to destroy 7 chromis. He doesn't bother the mandarin or clowns, but hunted and wrecked my chromis group.
I would think your tank size would be fine, provided you do not have it pack with rock and coral. My fish, at least seem to greatly prefer swimming in the open water. While the female is a bit shy, I have yet to see either dart to or through a hole in the rocks, just gracefully cruising above them.
I will try to get a pic up, but I am having difficulties.
