After the last posts in this string I stopped using HM FAP and switched to HP Pro Satin as the FAP could give me head stikes even in the high printing position. I also bought a humidifier, the one Andy suggested, and could get the humidity up to ~30% when the baseline was ~20%, better but still a little out of spec for the paper. In any case the HP Pro Satin is so good that I had no reason to go back to FAP although I reasoned that I would some time in spring when humidity hit 40% or more.
Recently however as I mentioned in one of the gamut posts, HP sent me a custom paper file for HM FAP. It's an OMS file that is uploaded to the printer and it included an ICC profile. I installed it last week after installing the new firmware and the new suite of profiles and this weekend I thought I'd give it a try. Humidity was 35%. In spec for this paper but at the low end.
After calibration I printed 3 images, one from Antelope Canyon, a new one taken over the weekend, and a black and white taken many years ago. All on 24" wide roll paper.
While I didn't print any images with strong, pure reds the colour that I was getting looked excellent. The antelope canyon print looked as good on FAP as the copy I made on Pro Satin and it has deep purples and orange colours. The new image matched my screen well. Neither showed an out of gamut areas and proofed very well. However while printing I could see that the paper was still bucking significantly, and while the 1st 2 prints came out OK, the 3rd print, the b&w, had a single 6-7" long head strike pattern close to the centre of the print.
So...back to Pro Satin.