Here's what I get, virtually identical to yours: http://paulwhitingphotography.com/utility/index.html#curve.jpg
So if my curve is ok, don't we get pointed to a faulty cartridge? or something else?
As for ink settling, I do shake my bottles (small 125ml bottles) of the various dilutions before refilling my carts. (I'm using the home brew variety of Eb6, aka C6, carefully mixed with an Ohaus scale to .1 gram). I believe I heard you say at one point that with a desktop we don't need to remove the carts and shake them before printing because the back and forth movement of the carriage is sufficient.
I'm very happy you've joined this thread... I'm hopeful we can get to the bottom of this!
Regards,
Paul