It is finally there. This editorial took plenty of time mostly because I couldn't decide what to do with this problem (Besides of the usual time I needed to actually learn the solution, involved doing my best to understand google translate of Russian text...). It uses this idea to rotate everything 45 degrees. An idea that was already a bit of a logic leap back when it was used as the central idea to a division 1 hard 4 matches ago!. And now it is used as just a secondary step in div1 medium? That is odd. So I tried to look for easier solutions. But the easier solution is a bit harder to prove. Of course, my eternal headache does not help either, but I am getting used to it.
It is a fun problem, I would have prefered to see it with a bit larger constraints (so that easier solution does not work) and as a div1 hard. But in a match that is not mere 4 matches after SRM 573.