Hey Polybus, great questions. I'll do my best to answer them.
For the terrain blocking line of sight, that is meant more for buildings and hills (similar to the
ETC rules set). You can see through a forest normally.
For comp 10 and 12, you would only be able to enter the folding fortress. Other buildings in the table are for scenery and not able to be occupied.
So yes, this means that monsters live a little longer if they hide behind a building or hill. but war machines will still deal their fair share of damage