@geoffl Oh, very nice! So now we have two ways of making the result obvious :)
I had been pondering writing a renderer in order to make it easier to play around with ideas for finding matrices for the higher-order snowflakes. I have a hunch that the matrices will need to have fourfold symmetry like this one does. I suppose really though the first step should be emailing Sébastien Labbé to find out how they discovered this one.