The problem is partially solved ! I had a parity error in the profile.
Now all is going OK, except the fact that Epson R1800 is bullshit, the same tif file, printed in exactly the same conditions (same paper, same profile, nozzles checked before printing) gives two different images, i.e. fairly more contrasted and a serious blue cast (one was printed one month ago, the second today).
You can rename a profile’s internal name by modifying the “multi localized description strings” string for spec 4 profiles or the “Localized description strings” string for spec 2 profiles in the ColorSync Utility.
As for the R1800, that’s a great printer that, aside from ink clogging, should be very reliable and consistent like other Epson models. The red and blue inks do improve the gamut especially with dark, saturated colors. I think that printer’s strength is glossy color work.
The problem remains still the same : impossible to have same print quality over time ; the prints are fairly darker with a blue colored cast when I leave the printer unused for some time (one month or more - the nozzles are checked before printing) it looks like it is a sedimentation of the pigments particles in the cartridges !