_,,,^..^,,,_ said:

The coarse grain (that I called 16mm just to remember...) is actually the 35mm downscaled...

I'm aware that the "16mm" grain covers better the DNR, but it seems to me a little bit too coarse... maybe I should try something in the middle.

Yes, that 16mm grain is far too much, not a good look IMHO. The 35mm grain, while much better than the 16mm grain, has the problem that it doesn't do enough to hide the DNRed nature of the UHE.

You should do a test with grain double the size of the 35mm grain you just used if you can, see how it looks.