Interesting. I wish I had that kind of success. I brew in 6.5g Italian glass carboys (smooth sides), use 1 oz of PBW in room temp water, and if there's even a hint of a krausen ring it never gets cut. Really all the Mark II does is shoot a singular stream straight up and relies on the "trickle down" of the cleanser to get the job done - which works surprisingly well on my corny kegs but simply doesn't work well on the carboys.
One of these days I'll try adding a small spray ball (has to fit through the carboy neck, so ~29mm max diameter) positioned down low where it can directly attack the krausen ring, and see what that does...
Cheers! (and Happy Fourth to you and 'Murricans everywhere!

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