Well, If you think about it, everything seems smaller than it actually is in game. The energy sword is (if I remember correctly) 6' long!! That's as long as I am tall. Chief alone is as tall as William Wallace. He raped considering the average soldier back then was around 5'-5'5" tall. And yeah, the Hunters hunch of really far and retract their necks like a turtle. They cover virtually all of their exposed areas.
Side Note: Every tried killing a hunter with a sword? Most frustrating thing in the world, but possible!!