Digital BW, The Print

I've had a curious experience playing around with a C84 and the MIS EZ inks 
in cartridges.  I've found that Paul Roark's suggestion for printing on EEM 
with the driver set to Plain Paper, Best Photo, and reduced Brightness and 
Contrast, does indeed produce a darker black in the shadows (visual 
analysis, don't have a spectro-whatever) and a slightly darker print 
overall than the same image printed selecting Matte Heavyweight paper and 0 
Brightness and Contrast adjustments.  However, in one of the images that I 
used to test various combinations of neutral and warm cartridges, I got 
distinct banding in the areas that I'd estimate are around 95% 
density.  (Nozzle checks are fine before and after the print.)  These bands 
also appear in the same area when I rotate the image 180 degrees (which 
suggests to me that it's a driver issue, not a mechanical issue) and they 
do NOT appear when I print the image selecting Matte Heavyweight paper - 
both high or low speed show no signs of banding.

I've about decided to do my printing using the Matte paper high speed 
setting, and building in a bit more snap by setting Brightness -2 and 
Contrast +2.  But I'm wondering if there's an obvious explanation for the 
banding when using the plain paper setting?

Cheers,
Kip