Thanks Ricardo for you patience.
The problem with that page is the low Cd of 0.2; while I see in literature higher values (see also on my page of my literature study of Cd). I am still totally not understanding all these things.
That is why I tried the (similated) empirical: compare a stacked cylinder with Perforated plate and Darcy Forchheimer medium and see when their behavior in wind velocity was the same (and that is the graph I derived).
So I am now using this emperical way, but I still don’t understand the formula behind it (and thus not the dynamics when I change eg the height of trees).
I think I will step down on this for a few days; see if time will provide me with some more clarity;-)
At this moment I blame myself for not understanding it yet. Thanks again for your patience.
All the best,
Victor