Forza 7, Xbox one X, HDR calibration

It would be nice to get more precise HDR adjustment/calibration setting. I suspect current one sets max white to some value that is more than TV is capable(for example 4000 nits) for reference and then user adjust towards that to see what is real max (TV clips brightness from some value, so for example after 1000 nits all looks same, → reference and user adjustment “match”)

Point is that lot of TV’s do some dynamic adjustments in that kind of adjustment screen and end result in real game image is not best possible. For example my Sony xe9305 seems to self adjust brightness tonemap while I fiddle with HDR slider, so adjustment is not best possible.
I understand that TV tries to be smart and to tonemap wide brightness range. I could be wrong how Forza 7 does this but still test image itself driver TV to do dynamic stuff (And yes, I have disabled dynamic settings from my tv, still it tries to )

As a secondary adjustment would it be possible to use few actual Forza 7 gamplay still images, night, cloudy, sunny, each with some highlights (sun, lamps…) to fiddle max nits value to point where it is just in top of range, not over, not under. (Bit like Gran Turismo Sport handles HDR calibration)