That's just the way I'd do it. For me I think I would see the spaces for the diagonals and 2x4 and so on more clearly if the squares are blank. There's absolutely no mathematical reason why this should work, and I am dubious, especially given the large drawdown that Dane reported - and then disappeared! But as far as a system for selection is concerned, it is as good as any and does at least force some structure on your play. That by itself is a good thing.