How does War Banner Phys Increase work?

Nearby Enemies take (8-11)% increased Physical Damage

That's the tooltip of War Banner. Does that mean that my aurabot is going to give a flat 11% increase in phys damage (meaning that instead of dealing 100k dmg to enemies, my allies will deal 108-111k dmg to them) or does it just add to the already increased phys damage nodes of my allies?

https://pathofexile.gamepedia.com/Damage_taken

Like all other sources of increased/reduced, war banner's increased is additive. A few examples/variants of this are shock, fortify (reduced instead of increased), vulnerability (physical, just like war banner). As usual if no other modifiers to damage taken are on your enemies, then it is like a straight up 11% more damage.

In summary: since sources of increased damage taken are pretty small since dyadus nerf, it is fair to approximate them as just more damage.