One of the reasons you might be having problems is that by changing the base, you are also changing the Dmax in relation to the cross over point with the next darker ink. That will cause the bumpy gradients. You can also use the Gray_Overlap= setting to have ore coverage from one ink to the next. that helps smooth out the bumps as well. You will need to increase the gray_gamma= setting to offset the affect of more ink coverage. I generally increase the gamma = to whatever the over lap is. ex: if overlap is 30, then I set to gray gamma to 1.3
You should really be building the profiles from the ground up if you are using this system. I know paul published a lot of profiles, but printer inconsistencies and changing variables can lead to lots of head scratching and wasted paper.
I realize you have an exhibition coming up and you need to get this done and don't have time to start from scratch so I put your string of measurements through my gray curve correction tool and it does show some flat spots that are causing the problems with the linearization.
He is what I would like you to do: Go back to the original settings you used to arrive at the values you posted above.
Then paste this correction curve into the Gray_Curve= Line of the ink descriptor file or the QTRgui if on windows.
Gray_Curve="0;0 5;4.05599831320583 10;5.81168282623405 15;6.86958377192356 20;7.92748471761307 25;8.98538566330258 30;10.1135596386264 35;12.8888948263984 40;15.4232935086374 45;17.1919298909369 50;18.9605662732363 55;21.1542328852923 60;23.9537540596557 65;26.976615916733 70;30.2246523942801 75;35.9840258718894 80;42.6969114298816 85;47.7881364295635 90;53.0896043260779 95;61.5658591072947 100;100 "
Then delete whatever you have in the Linearize= line.
Then print your 21 step target again, measure, and the linearize with the new readings (you must always keep the gray curve values in there as well though)
That should smooth out and linearize the profile. You can find that correction curve tool here for future reference: QTR-Correction-Curve-Tool
Hope that helps.
Richard Boutwell