The map I was playing had a scenario involving booze and a Mafia hit man stealing it so they didn't have to pay tax.
There were some small buildings that I started between. I suspect they were car garages.
One of the Mafioso was shooting through the side of the garage. I think he was ignoring the roller door. Then, once he's ignoring the roller door, the inside wall of the garage probably isn't taken into account in LOS calculations.
My characters did not have LOS to shoot back at the guy (because they were facing a wall).