This is cool! The simulator was useful for understanding what was going on, I hadn't realised until I watched a few that the roons can push marbles out in between squares.
Thanks! Glad to hear the simulator was worthwhile, took me ages to hack it into shape.
I did actually experiment with adding markings on the edges of the path roons, so that when you put them together, the "phantom channel" becomes visible. Ended up looking pretty cluttered though so I scrapped it.
