When originating from lower ground ranged attacks may be blocked by decorations on a higher ground. This effect can be seen on Alien Vendetta's MAP31: Killer Colours at the beginning of the green section where fireballs from the hell knights are blocked by the base of the green torches. This effect is also seen in some Dwango5 levels.
The obstruction occurs because decorations have a height of 16 according to the engine. Since the graphics of most decorations are taller, projectiles and shots normally pass through them unless they are fired from below and intersect the decorative things 16 units or less from the floor.