For that size room you are better off with simpler broadband absorbers in the corners. Look at the paragraph in the beginning of Ethan's article:
Please understand that the bass traps described in this article are intended mainly for larger rooms. For rooms smaller than 25 by 15 feet you'll usually do better with broadband bass traps made from thick rigid fiberglass placed in the room corners. This is described in my Acoustics FAQ linked above. Once all of the corners are treated, then it makes sense to consider adding bass traps like these flat on the walls.
