If an enemy is firing at archers behind an invisible wall with arrow slits what bonus would the defenders get? +8AC with a 50% miss chance?
+8AC for the arrow slit
Add a 50% miss chance for the invisible nature of the wall?
What about if the slits were shuttered with an iron shutter? A wizard could use an open/close cantrip to shutter-up the slits immediately after the friendly archers fire.
