I tried around a bit more...
I can now import and properly reexport the forest files - if i attach the original offset list to it, it work as it should - trees get cut, trees get adjusted to hills...
If it try the same with a file of my own - like a collection of boxes, to represent ruins - it doesn't work
There is another effect: the very same Offset List apparently also causes the trees meshes to be distorted and sway in the wind... While the distortion (it's minimal) is something we could live with, the movement of the sway is noticeable enought to be disturbing on ruins...
And yes, while the boxes i export do not get cut on roads, nor adjusted to hills... They do sway... (And they do cease to do so, if i remove the Offset List from them...)
There is something really phony about this all... I am sure the Offset List has to do with this (Because removing/reattchaing it on the original tree model has the expected effect)... But i am also sure i am missing something (Because removing/reattaching it on new models does affect Sway but does not cause Cutting...)
I would really like to know, what exactly these coordinates are supposed to hit.
Do we see any way to disable the sway from XML ? because from what i see now, i can't have Cutting without sway on the nif side...