i don't think the amount of times melee move out of range during a boss fight is close to the number of you have to move....
Most boss AOEs either target all dps, randomize between non-tanks, or aim in a direction.
First scenario, everyone has to move, and circle aoes don't always surround the boss so the melee may have to move or miss a positional to keep hitting, but most of the time they can still keep hitting.
Second scenario, there are melee and ranged specific aoes, and while in older content there were more melee specific aoes, most HW content targets both ranged and melee pretty evenly.
In the third scenario, if you're unlucky to have the AOE face you, and this aoe is a cone, the AOE is smaller the closer you are to the boss, so melee only need to shift a bit, whereas if you're a bit further away, the safe zone may be further away depend on how close to the center of the aoe you are.

Also I am not very collected at 4am. Feel free to correct me. XD