Sprite depending on Player's position

Unity Engine
1

Hello.
What would be the best solution to make object’s sprite change depending on player’s position?
I have a 3D World, but my enemies are flat 2D Sprites facing camera (bilboards).
I’ve prepared 4 sprites for my enemies (back, front, left and right) and I’m wondering how to make them change depending on where player stands.
i.e. When enemy is going towards us we see his front, but lets say that enemy is going same direction, but we’re standing behind him, we would see his back.
Should I just use couple of conditions checking where my player is, if distance is shortening or not etc?

2

is bump working?

3

This might help GitHub - unitycoder/DoomStyleBillboardTest: Shader to display camera facing billboard, with different texture based on player position angle