You’ve got it exactly right! Look bite the videos that I have sent.
Let’s try it this way. I will not be able to explain this mathematically, but as I understand it as a layman.
This is the initial situation without filmic:
Shematically, I only transfer a part of the dynamic range of my camera to the sRGB color space:
Now, I have also set filmic so that there is no compression. The look of the photo does not change almost at all:
If I now increase the exposure by one EV, the shadows are getting lighter and I get the warning that I have left the sRGB gamut in highlights:
So, we have this situation now:
Now with white relative exposure I bring the highlights back into the gamut. (Note that the shadows are affected because of the compression):
Now we have this situation:
Now I want to expand this darker compressed area a bit with black relative exposure until I have enough contrast in this area:
This is how it looks now: