Fearful is applied by Zorn and has a 30 meter radius. Your DPS, at one point or another, are going to get it. They have to recognize it and be careful during transitions.
You are partially correct.
Zorn will do the fearfull effect but it only goes to 28 meters. So if you have the info enabled on the target nameplate icon you can see your exact distance. The tank can keep still until the red circle aoe phase which then everyone has to run it is best to run out of range and barely into it to keep fearfull from applying.
Furthermore, if you have your ranged on Zorn (30m-35m) then it will be easy to never get fearful during the whole boss fight unless you are careless and get to close during the red circle phase mania.