If there is step access to a building e.g the back of the supermarket you can jump into it (not from the steps but from the side) and you will be in the floor, it is possible to go prone in this position and literally be hiding in the floor where you could easily pop up and kill any would-be shopper. I'm sure sure if you can do this on other buildings with a simlar layout, my guess is you can. I saw a guy in the floor the other day in the building with the prison cello downstairs found at military bases/bolota airfield.