When Shangalar and me years ago early in dev process went through all sceneries in order to streamline the vision and movement blockers, we decided that every scenery which is roughly above waist height should block vision like a wall, because we noticed that we did not have a whole lot of sceneries to work with if we wanted to provide people with "shelter".
Only years later did Lidae come up with the cover system which has given us another angle on this issue and I'm interested to hear what people think about Cars, as many of them are of the same height as barrels or crates yet they block vision and thus dont provide cover.
For lack of a better word, Shang and me refer to a vision blocking object as "shelter" and to movement blocking items, with cover triggers for the hitchance malus as "cover".
Of course if we turned all cars from shelters into covers, certain maps will be reviewed again and might have other shelters placed to compensate. This affects only cars, al the trucks will still block vision as theyre quite tall.