We have to respect the total ink limit of the media and we try to bring it as high as possible by adding the long trailing ends of our curves. These trailing ends reduce noise, eliminate dots, allow for the curves to work on a wide range of printer conditions. The black line is the total ink.
Shade 5 is the meat of the mid tones and you can se that it is the ink which prints the most on its own over range starting strongly about 40% to about 75%. The actual shade 5 curve begins printing about 12% and under prints 100% dMax.
For split toning the best agent of change is shade 4 and you can see how it influences shade 5 as it comes into the mid-tone. This is where shades 2,3,4 are one ink tone and 5,6,7 are another.
Likewise, shade 6 is a good split tone ink for the high end as it comes out of the mid-tone - this is where shandes 2,3,4,5 are one ink tone and 6,7 are another. Shade 5 can also be mixed 50/50 between the two ink sets to make a very gradual split tone. Special Edition are blended ink positions in shades 3 and 4 and then a hard split at 6.
You may be surprised to see how little black ink is used - where as we depend more upon shade 2 for dMax. In order to have exceptionally long smooth tone without visual dot - the tails are necessary. But they accumulate total ink and the black is very difficult to manipulate. Too much ink and the dMax begins to lighten.
You can right click on the Windows version curve while in QTR GUI and view it!