Hello,
I don’t remember if there is a way to directly ignore instigator but if no better idea is given, this way would work :
With overlap instead of hit you can use “cast to” to avoid only the instigator.
Create a variable actor BP, and a custom event / function to set it.
When you spawn your projectile in actor bp, from return value output drag your custom event and use custom event / function to set variable with instigator. Then you can compare it with your other actor output.