Invader will come from 1 of 2 spots before boss then its 3.

You can predict them. Did it last night. Kelly's grave Primevil had spawned This invader spawned on the left, Dropped him Went to middle spawn (although it's slightly to the right tbh) Waited at the back and boom! Invader Infront of me Dropped him and rotated to right side Low and behold he spawned on the right side, dropped him. We lost the match, but that's not the point. You can predict the invasions after the first one has taken place (the only one my team can't predict yet). You can get this down to a science if you really tried

The zone is random, but the point within each zone is fairly static. If you know where those spawn points are and can read the bar enough to be in position at the right time, it's actually fairly predictable. Even if I'm playing solo I easily score 2-3 invader kills in the manner I describe where they spawn in right in front of me and are taken down before they can even get a clear picture of where they are. It's by no means fool proof unless you play with a coordinated fire team, but so long as the other team invades whenever their portal opens, which happens 90% or more of the time, it's pretty easy.