So been testing the purge out and so far it rarely fires.
Only after adding the purge anywhere mod in did it start to work.
However, it was buggy…mobs would attack the walls then port inside the walls or on top.
So I removed the mod. Tried again. I actually got the purge to run however the mobs are still porting in between the outer walls or on top of the walls.
I guess they have ladders or secret tunnels they are using