Hey Gilles — great to see these studies you're doing. I think you're getting the main gist of it but if I could offer any advice it would be that the key to a successful image is to have shadows in one value range and the highlights in a separate value range.
You're getting this in a few of your studies but in the old western man, for instance, the sunlight that is being cast on his face is much too dark (and close to your shadow values) than it is in the photograph. Now that doesn't necessarily mean the shadows have to be super dark and the lights have to be super light — you could render everything in the shadows using a 40-70% black, but if you then rendered the lights using 10-40% black they'd probably look too close and muddy so you might just overexpose the lights a bit to make a better 'read'.
Apologies for a bit of a rant, hopefully the above makes sense and helps in some way.
You're getting this in a few of your studies but in the old western man, for instance, the sunlight that is being cast on his face is much too dark (and close to your shadow values) than it is in the photograph. Now that doesn't necessarily mean the shadows have to be super dark and the lights have to be super light — you could render everything in the shadows using a 40-70% black, but if you then rendered the lights using 10-40% black they'd probably look too close and muddy so you might just overexpose the lights a bit to make a better 'read'.
Apologies for a bit of a rant, hopefully the above makes sense and helps in some way.