All attacks are simultaneous so the rubble is not there when KK11 is attacked.View attachment 9296
Per G14.661 BUILDINGS: A Multi-Story Building (B23.23) that is also multi-hex can create Reverse Slope hexes as if the building were a hill of the same full-level height.
What happens to hex KK11 if KK10 is rubbled? Is it attacked during the same fire phase?
Not aware of any rule that says OBA attacks are simultaneous. Not aware of any rules that say OBA rules are not simultaneous either, but I would consider that COWTRA means following the mechanics as given, i.e. the effects of rubbling a hex may open the possibility of attacking another hex.All attacks are simultaneous so the rubble is not there when KK11 is attacked.
Once it is rubble, KK11 is vulnerable in subsequent phases of the same turn (rout, advance etc.)