QTR-Quadtone RIP

Roy, I understand your answer about limits being percent of ink. But
your response about density I still don't get:

"Density is for relative density of a lighter ink compared with a
darker ink." 

I have a specific purpose here: On my Epson R2400 I'm printing to
transparency film and want the range of tones to be created more by
"specs" of black ink and less by a continuous tone--so my print looks
more like a random pattern bitmapped image. That's part of the reason
I'm using 720 DPI. 

I use the transparencies to expose photopolymer film for creating
etching plates. What creates the tone in the print are the specs of
black, which translates to texture on the plate, which holds the ink.
The more, or denser, the dots the darker the tone. 

What's happening now (using one of the warm curves), is that I'm
getting blacks in my print, but the mid-tones and hightlights are
dropping out, and when I look at the transparency I see the darks are
made of dots and the midtones and highlights are more continuous
tone.--I want more "dots" in these areas. 

I'm considering, then, upping the limits (percent) for my black ink,
and lowering for the light and light-light black, but I don't really
understand how density works in the equation.

For example, if my light black ink was limit 50/density 30, what    
happens when I change density down to 15?       

Best, David.