Digital BW, The Print

Hi,

I'm fairly new to black + white photo inkjet printing, and I'm 
beginning to get 'good' (/better) results from most of my negatives 
using the following settings on my 1270 loaded with the MIS dye-based 
color inks:

negatives scanned @ 3200 ppi, 16-bit grey (Vuescan)
Mostly TX, some PX and HP5 (and even some ASA 1600 Kodak Recording 
Film)

black only
HWM paper
1440 dpi
working space dot gain 20%
printing @ dot gain 30%
gamma 2.2
color adjustment ON (but no adjustments made, i.e. brightness and 
contrast both at "0")

After scanning I make Curve adjustments to the overall picture, and 
to subselections based on an 8-bit duplicate for shadow, highlight 
and mid-tones (sometimes mixtures), as well as to specific, manually-
selected picture areas.

A few of the images print 'perfectly' but most have problems with 
deep shadow detail: I can either print them with good shadow detail 
up to about 95% black (leaving the picture kind of flat), or if I try 
to go for a deep black, the deep shadows are 
clogged/clipped/posterized, with very noticeable black patches in the 
95 -- 100% (roughly) black range.

I have tried a couple of workarounds including applying dithering to 
the deep blacks, but although this is better than the black patches, 
it still does not quite make for a smooth, natural-looking tonal 
range. Printing at <30% dot gain aggravates the problem.

Thanks for any suggestions!