I don't disagree with Jon Cone about the low frequency dithering. When I look at the dithering pattern with a magnifier I can observe a low frequency pattern in the very highest highlights (98-100%) of the negative, but in printing that becomes the lowest shadow density of the print and the dithering pattern becomes invisible, thus it is a largely irrelevant issue for me. Great separation in the print highlights (negative shadows) is a much more important consideration for me in making digital negatives, and in that regard the single shade, single curve system works very well.
BTW, although the topic of this discussion was ink low limit, the major design consideration in my profile is that my ink set uses six inks of the same shade, thus there is straight line UV absorption, from the lowest shadows to the highest highlights. So the low frequency dithering issue aside, the Carbon 8K-12 profile is producing what is essentially a continuous tone negative with straight line output, which is very easy to adjust for transmission Dmax.
I pull the PK inks from 220 ml Epson K3 cartridges. Another approach would be to try the Cone UV opaque black, which is said to dry very fast and could possibly be even more opaque than the Epson PK. So far, however, I have found the Epson PK to be the fastest drying and hardest setting ink out there, and those two issues are of great importance in making digital negatives on Pictorico, especially if you are using one of the small printers with those pricked wheels that guide the media.
Sandy