Ecosolvent DX4 head, Roland SP300 strange banding

[levasc]

This is not inkjet related, and seems very specific, but maybe someone has encountered it.
I always thought that the banding is due to cloged nozzles of magenta
Here the head printest for cyan is ok:

But I noticed that banding seems to be caused by the cyan printing beyond image here:

You see, the ink drops printed beyond the image, the pattern is repeated all the way up.
And at the same level of ink protrusions, on the image the blue is lighter than other places, since part of ink used beyond the image. Hence the banding. Head seems ok for cyan.
What could be the cause of this banding?

 

[levasc]

From photo it seems ~4 protrusions every 1 inch. As I understand the DX4 head (probably) printing width (height) is 1 inch. The draft printing (used draft) is 8 passes (bidirectional). So every 4 passes go in one direction... maybe it can be related to mechanics (or electronics?)