Digital BW, The Print

I'm trying to understand the black art of B/W inkjet printing (with MIS sepia mix inks and Paul Roarke's curves, on an Epson 1280 using EAM paper), and am puzzled by some of the effects I'm seeing and mystified as to how to control them.  Some images print beautifully with no tweaking at all; others exhibit unacceptable "banding" or "posterization" -- areas that come out almost flat and featureless in the print, even though the screen image of the scan shows plenty of detail and tonal gradation. 

I've read through some earlier discussions of related issues on this forum, but I haven't been able form a full picture of what's going on or what can be done about it.  I did try printing out some grayscale test images, but to my (completely unpracticed) eye, they look fine: there is no visible "clumping" into bands.  I also tried the multiple-layer process suggested by workmantx (in message 18047) on one of the images that shows posterization most severely.  This yielded a big improvement, but (a) I'm unclear as to *why* this process should help, and (b) in any case the print still has some noticeably posterized areas, with much less detail on the paper than is visible on the screen.

Some previous posters have asserted that these problems are entirely with the curves (but without explaining further, as far as I've been able to find); in this case, the options would seem to be either more (random?) experimentation with curve adjustments, multiple layers, etc., or else a different method (e.g., the Piezographic driver) that offers a more direct translation from screen to print.  But I also wonder whether some of the problem (in particular, the loss of detail) could be coming from bleeding of the inks on the paper, in which case the answer might involve changing inks or paper.

Can anyone help enlighten me further or point me to more in-depth information about this?  

Thanks,

	Benjamin