For large area burning I use a single piece of flexible black paper. Since it's flexible I can bend it, and when I subsequently tilt the paper so it isn't parallel with the paper surface, it forms all kinds of different shapes.

I almost never find the need to burn in small areas, but when I do I use a combination of my hands and a piece of board with one small and one large hole cut in it. I've used them maybe a dozen times in all these years.