FPS: Zombie overlap not recognised from behind

After trying to use more sophisticated methods to start and end taking damage from my zombies I’ve reverted to the more simple approach.
So when my zombies detect me they chase and catch up with me. I want to use the Begin and End overlap events on the zombie blueprint to do damage to the player. I’m just using a print string at the moment to show when the zombie does damage and stops when I run away. Works fine from the front but… when I turn my back on the zombies all overlap events stop being detected.
I hoping someone tells me there’s a built in function I’m not aware of…

Looking forward to your guidance!

Ray