The multiblock scanns in a certain pattern. Collums down ->up, rows east->west and these south->north. So with the changed casings you can see how far it got before it failed. From the patters i would say once hitting the center with the scan, it failed somehow. So there it must hit a not accepted block somewere.
In case you can somehow understand code: https://github.com/Blood-Asp/greg…seOven.java#L84