Just to make sure I’m on the same page, I notice that your attachment is using the 21-step Scanner Tool. Are you using this instead of the 129-step Smoother because you don’t have a spectro to read it? Or are you using it to try to make a manual adjustment? (On my first reading I thought you meant the latter, but now I’m not so sure!)
I have a couple thoughts on this. First, using a scanner to calibrate the process is nowhere near as accurate as using a spectrophotometer or densitometer (though there is no support yet for densitometer readings). I think that the intention is that the 21-step tool will eventually be densitometer compatible too. (Walker!) Second, in my experience with PiezoDN so far, the first round of the linearization process gets you fairly close to linear but not all the way. A second iteration gets it almost perfect; probably as close to perfect as it is possible to get with a hand-coated printing process. Making an ICC profile from the linearized .quad brings the whole range down a bit (darker) for reasons that Walker has explained to me but that I don’t quite understand. Personally I don’t like the effect of the ICC. If you need to manually adjust the curve for a particular look that you are after, try using the Piezography Curve Adjustment Tool which allows manual control of the curve similar to a Photoshop .acv curve.
One comment about terminology. To bring a tone or value down means to make it darker, not lighter. Think turn down the lights! Down does not necessarily mean a smaller number, nor does it necessarily mean lower on the graph. For example, with Density values that you might be familiar with a lower number means a lighter value, but with Luminosity (L* - the L part of LAB) it is the opposite - a lower number means a darker value. PiezoDN uses L* values.
I am a long-time (20+ years) densitometer user, and it was not easy for me to switch, but well worth the effort. I have also recently figured out how to convert both Density and Luminosity to percent in order to compare them, and they are definitely not the same. I was always needing to manually lighten a linearized curve based on Density, whereas Luminosity based linearization looks right to my eyes.
Please forgive me if this is stuff that you know already, but it may be useful to others, too.