Hello again,
thank you all for the replies.
Erik, I have already presented the best results I could achieve. I may be wrong, but it looks to me like the mean error gets bigger, not smaller, if I dial back the saturation.
Thanks for the recommendation of Adobe DNG Editor. Brilliant!
Rhossydd, I'm sure to try out what you suggest.
At first I understood you as saying that the Passport chart itself is more saturated than other X-Rite charts, but I think (and hope!) you're not saying that