The multiple shots about sniper nest show, his rifle has set position to cover area around hot dog stand and covering area is very narrow because of opened only last bottom slot in louvers. However, when Liberty's husband killers (and later from CIA) start shooting on Liberty from building roof or top car park level, Joe found them in his sniper scope and hit them. The view from scope showing picture, that rifle is on same level or below of target, but for such angle sniper would must change angle of rifle to position, where are closed louvers. And he definitely would not move louvers, it would reveal his position. Especially when all SWAT snipers was around.