Patnor,
That's an interesting article.
The funnels I used in my processing days were made by Nalgene, and intended to use round filter paper. I expect the included angle was 60°, although I am not sure. In order to achieve a proper fit, the paper was folded in half, then in half once again, so 90° of the circle remained. The paper was then opened, with three layers on one fourth of the circle, and the balance a single layer. I suspect the approximate 10° noted is for use with funnels of a different included angle.
I'm curious about the recommendation to tear off the corner. To my knowledge, it serves no purpose and offers the threat of overflowing fluid past the filter paper. Do note that I had a secure setup and often filled my funnels to the top, disregarding the admonition to fill them only 2/3 full. The top third holds a huge amount of fluid, so it bought me time in my extensive filtering operation.
Harold