So I thought I would just share this as I found it interesting and depending how good some of your BG mates might be, you could use it to your advantage for helping others.
In our war today, the BG i'm in had the Siphon tactic selected that we were to face. I usually check which tactic the opponent chose by clicking on a fight in my path to check the associated nodes. When I did, it didn't show any tied to the defense tactics... But when I clicked on the Global icon on the right, it showed Siphon was active but looking at the map further, the boss node was empty. This caused Siphon to not be active for
ANY fights showing that the boss being up is tied to the Defense tactic.
https://www.youtube.com/watch?v=MFcxY0aylRQ