I'll have a bit of a play tonight.
BTW, the main display is a 1080p projector (old Epson TW2000 - same as the 1080B).
The reason I'm so keen on getting into calibration and HCFR is that the pj has a full CMS including a gamma that can be manually adjusted.
Also because the home theatre is in a completely blacked out room, I was thinking of aiming at a higher gamma than 2.2 or 2.22. For instance, BT1886 looks like it would suit a light-controlled room (but I'm getting ahead of myself, aren't I?).
Had a play around with HCFR. Took me awhile to figure out how to bring up the windows,etc. you talk about.
However, I was only using my personal computer's screen as the display, which (as far as I can tell) doesn't have the high and low range controls. Not sure whether I should be looking at the controls in the monitor, or the controls for the video card (Nvidia).
Tried your preliminary method on my Projector, with HCFR running in my HT computer (Nvidia GeForce GT1030 video card).
When running the 80% or 30% continuous tests, the R,G & B levels were moving up and down slightly as each test ran, which caused the dE to fluctuate madly from 0.2. up to 3.7!!!
Adjusting the R,G and B levels, didn't appear to have any effect, for both Gain and Offset (Epson call Bias - "Offset").
Not sure what I am doing wrong.