Common sense answer; Certain actions get a bonus in dmg being done from the flank or rear.

Example Trick attack with Ninja;

Delivers an attack with a potency of 240.
400 when executed from a target's rear.
Rear Bonus: Increases target's damage taken by 10%
Duration: 10s
Can only be executed while under the effect of Hide.

Smart people read and learn the jobs and see their benefits; https://na.finalfantasyxiv.com/jobgu...gn=na_jobguide
Most players think they know their job when in reality can't even handle simple actions. No offense, but they know who they are -.-;

Most people lacking common sense and apparently don't know their job; It does not matter you hit them anyways and not enough to make a difference in the long run.