After a bit of experimenting I decided to create a patch set with a much larger set of neutral and near neutral patches. I combined this with a standard grid of 9x9x9 (729 patches). The near neutrals comprised of 1546 patches.
I duplicated the near neutral patches and added the standard grid patches and randomized the set. This made 4 pages of letter size Isis targets.
I made profiles for both Canson Rag Photo Matte and Costco Glossy and printed several targets that comprised of the Colorchecker colors and a neutral ram from L*=2.5 to 100 in steps of 2.5. Each had 2 additional duplicates that were also randomized. Since each set had 64 patches there were a total of 192 patches. These targets were in 16 bit Adobe RGB tif files Isis readable and were printed using Absolute Colorimetric Intent. Only in gamut colors were analyzed.
The results finally eliminated the Costco paper perturbations I was seeing in *b and the neutrals at last had lower dE00s than the more saturated colorchecker patches. Average dE00 for neutrals was .42 on each of the neutral colors and about .72 for ColorChecker's colored patches.
The Canson Rag Photo was even better, coming in at about dE00=.34 for the Colorchecker colors and dE00=.32 for the neutral ramp. So for the Matte paper this particular target patch set does a good job on both color patches and neutrals.
One note of interest is that the dE00 variation for neutrals exceeded the dE76 while the reverse is true for colored patches. This is one of the more curious aspects of color perceptual sensitivity. It's easier to see differences in color when the colors are neutral to near neutral and much more difficult as the colors become more saturated.
These are the results from the Costco Glossy paper which has more variation than good smooth matte papers:
2 Printouts, Epson 9800, Gostco Glossy
ColorCheckerColors dE00: 0.76, dE76: 1.35, Neutrals (Steps of 2.5 L*) dE00: 0.52, dE76: 0.43
ColorCheckerColors dE00: 0.64, dE76: 1.09, Neutrals (Steps of 2.5 L*) dE00: 0.40, dE76: 0.35
ColorCheckerColors dE00: 0.58, dE76: 0.91, Neutrals (Steps of 2.5 L*) dE00: 0.40, dE76: 0.37
ColorCheckerColors dE00: 0.83, dE76: 1.54, Neutrals (Steps of 2.5 L*) dE00: 0.51, dE76: 0.44
ColorCheckerColors dE00: 0.65, dE76: 1.18, Neutrals (Steps of 2.5 L*) dE00: 0.36, dE76: 0.31
ColorCheckerColors dE00: 0.55, dE76: 0.87, Neutrals (Steps of 2.5 L*) dE00: 0.36, dE76: 0.34
And these are the results from the Canson Rag Photo Matte:
3 Printouts, Epson 9800, Epson Enhanced Matte
ColorCheckerColors dE00: 0.33, dE76: 0.50, Neutrals (Steps of 2.5 L*) dE00: 0.29, dE76: 0.26
ColorCheckerColors dE00: 0.35, dE76: 0.51, Neutrals (Steps of 2.5 L*) dE00: 0.30, dE76: 0.27
ColorCheckerColors dE00: 0.34, dE76: 0.51, Neutrals (Steps of 2.5 L*) dE00: 0.31, dE76: 0.28
ColorCheckerColors dE00: 0.32, dE76: 0.49, Neutrals (Steps of 2.5 L*) dE00: 0.31, dE76: 0.29
ColorCheckerColors dE00: 0.34, dE76: 0.49, Neutrals (Steps of 2.5 L*) dE00: 0.31, dE76: 0.28
ColorCheckerColors dE00: 0.35, dE76: 0.52, Neutrals (Steps of 2.5 L*) dE00: 0.33, dE76: 0.31
ColorCheckerColors dE00: 0.35, dE76: 0.51, Neutrals (Steps of 2.5 L*) dE00: 0.34, dE76: 0.32
ColorCheckerColors dE00: 0.36, dE76: 0.56, Neutrals (Steps of 2.5 L*) dE00: 0.32, dE76: 0.29
ColorCheckerColors dE00: 0.35, dE76: 0.54, Neutrals (Steps of 2.5 L*) dE00: 0.33, dE76: 0.30
Each of the printouts (Two Costco, Three Canson) had 64 total colors duplicated 3 times, hence each of the groups of 3 lines. While the groups were randomized, the same tif file was used for each of the 5 printouts.
I have attached the Isis ready test 192 patch Adobe RGB tif file as well as the CGATS file of the 4 page Isis target from which the profile targets were made.