Cover and piece of scenery definition

I think your picture is a bit inaccurate, but w/e.

IMO if Daiyoukai had been touching the outermost corner of the building (the left wall of the stairs essentialy) - he would get cover. Otherwise - no.

As for treating buildings as one whole piece of scenery - ask your friend, whether Daiyoukai (red) would get cover from Orc (blue) in this case:


(green line - LoF from Orc, which shows that Orc sees less than 2/3rds of Daiyoukai

If he answers "yes" - don't play with him/her anymore =)

 

I would say that unless you establish that a wall section of the building is a separate scenery item ahead of time such as via means of a house rule or by simple agreement, your opponent was correct. The rules for scenery items lists wall sections, doorways, etc as examples of scenery items, but it also lists that access width can be assigned for parts of a scenery item meant for access so it is very possible a single item is a large building.

 

There is a widely houserule that goes something like this:

“A corner always breaks cover. A trooper can combine multiple pieces of scenery to fullfill partial cover requirements.”