I wanted to do the tests anyway, to understand a little more what's happening, why the contrast is low, how much should I increase the time etc. But I see your point.

For the fog however, I don't see why there should be more fog on a field exposed as zone 0 than on a field which received no exposure ( lens cap on ) ? That's the case in my test, and it proves that the light meter didn't give me zone 0 exposure (respectively zone V) but a little more (overexposure). Isn't that correct ? I'm trying to understand...

Thanks for the replies guys