Holy smokes, thanks for the effort! I tried to set it up as you did and in theory it works! Everyone gets registered and those too far away got sorted out. Buuuuuut for whatever reason they still like to chase one and the same target.
I created your logic, functions and all inside the projectile blueprint.
Not tidy, I know. But maybe it doesn’t work because each projectile instance runs through that individually? So what I think, and correct me if I am wrong please, is that some of the parameters need to be set in the character/turret blueprint or set globally?
What I also tried was to create the logic in the character/turret blueprint and assign the homing target via a custom event after a projectile is spawned, but that didn’t work at all.
But at least it looks like this now:
Yeah, I used a Third Person Character as turret 
Please ignore that.