DoVi_Scripts_1.8.4.2.beta now has a workflow (6-8-2) that can ''quickly'' export 5x FEL/MEL PQ screenshots. (will only work if your input is at least 36min)
It's random so just because those 5 screenshots don't show a difference doesn't mean there isn't one on another shot. Plotting DV and HDR10 is a better indication of brightness expanded via fel.
It's been a while since I tested this but the bt2020 flag with RGB tv-led definitely did change the colors slightly but nothing major really. And I when I tested that, it was before the @yusesoap profile8 era so I only tested profile 5 patterns.IMO that bt2020 flag is just a red herring. My Panasonic UB820 also sets it for DV.
If you have an hdfury device, you can remove it. I tested the Zidoo and Shield (they sent bt2020 flag too before) and both had different colors with the bt2020 flag.
Those other differences in the signal you found are very interesting though.
check your pmany chance you could PM me a copy as well?