Thanks again Lennart for your efforts.
I got it! It is obvious that the 1024 factor is there, based on my current tests. Thanks for mentioning it, it delivered me finally an answer. Which means there is something going on that is not correct at all. If I set the zoom to 100% and the render format to 10x10cm, then the cube with 10x10cm should fill the render area, but it doesn’t. (I had set up the resolution to 100 pixel per cm, to measure it in Photoshop)
Here I see the reason why I suggested the reference guide in my initial post (I shouldn’t have given up and suggest a workaround), as I did not got something correct out of a mathematical correct set up… I have done over years print stuff (with Illustrator) for a world wide producing company, with print houses all over the world, precision is key there. So this here is not acceptable… Go figure.
Thanks for the 1024 or the 102.4% zoom factor. It lead to the problem and I think it needs to be fixed . At least from my perspective. (I have filed a report, and I hope people file a report to MAXON if something is not correct, instead of using workarounds… myself included!)
All the best
Sassi