I didn't think of stopping freeze during the tutorial, but now it sounds so obvious when you've suggested it :) We were thinking about spatial positions, but because so often same note comes several times in a row it wasn't a good option.. And I didn't want the classic stream, wanted a bit more original... But I understand that it ended up being a bit overwhelming...
Maybe a good compromise would be not random but biased placement of notes - like "up" note appearing in up positions if possible, in central if not, and in the bottom only in the worst case (and same for other directions) - this would probably still work as a direction cue.