_,,,^..^,,,_ 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.

I agree. Way to coarse.

Can you double up the 35mm grain plate?

It might help you hit the middle ground, but it depends on what method you are applying it. I use Adobe Premiere / After Effects. From previous posts you seem to use AVISynth or other Free software which I have very limited knowlege of. Especially in overlaying a grain plate.

Out of interest is there any way you can copy detail from on source (MPEG 2 Blu ray) and overlay it on another (UHE Blu) like you colour match scripts?

In my eyes the main problem with the MPEG 2 Blu is the compression artifacts because the way MPEG 2 handles the grain, which is why you are trying the overlay film grain method I suppose.