this could be a more generell solution but you have to be carefull that your input geometry is one object - i created a bound box, extracted the highest surface, scaled it, move it up and used it for projection so it will allways be bigger then your input geometry
Thank you guys for your advice but that didn’t actually improve the result of make2D.
I have now figured out what helps to get a good make2D result! That is scaling the geometry up by a lot.
It might be interesting to look into double precision to get an optimal scale factor. But wierdly, changing the absolute model tolerance doesn’t improve the result, only changing scale does, which makes me wonder if that is actually relevant.
The results of my investigation also show, that make2D in rhino also works better with scaled up models. Thats quite the extra step when generating drawings. Fortunately it can be automated using Grasshopper.
Anyway, here is a screenshot of the final, actually desired and expected result: