I'm not sure that I know what you mean by purple circles, but:
I wrote those N and W designations on channels, you have 4 channels for each side (left and right) of the block. Every channel has 2 N passages, and rest of them (all) I meant to be W, even to connect the outers in every way, those blue lines, vertically and horizontally. By having 2 N passages per channel, think that you'll have equal flow through all of them, cos north and south one has 2 N same like straight ones...
Dunno...
