I'll clean it up a bit (the noise you're seeing in the picture is drybrushing), finish it , then with the chaplain since I've postponed it too much :).












Section 1 of the picture shows the brush stroking a corner towards the right side. The outer edge (or surface) is actually the surface that gives the most resistance to the brush and the paint on it at a "microscopic" level. Thus, most paint will rub off the brush on this edge of the corner. The tangent edge (or surface) hardly opposes the brush or the paint found on the brush, hence less paint will rub off it.
Scrubber brushes