Backstabber doesent work on back if shot from right side but works on shoulder from left side

[abc123xz7]

Depending on what side the enemy is compared to you getting a backstab might be really hard or shooting the shoulder in the side will be enough

 

[steventheeven3]

The item works based on your position relative to the enemy position, doesn't actually matter where you hit them.

 

[Gutszen]

I think this is likely a camera position thing. you peek left to right in this game so it likely counts all of that side as the back and the other still has view of your model