Yea, when you are talking about pushing a brick, it doesn't matter which side is down, but I can't imagine a rectangular string not locking up, for a variety of reasons. The first of which is that when the ball hits the corner of the rectangle, the opposite corner will dig in and the ball will exert a torque on the string, trying to roll it up on edge, which will further displace the cross strings increasing the normal.
I would love to try a set, and see what it does, for science if nothing else. Maybe I am totally wrong and the stuff works. Wouldn't be the first time.