This might help.https://community.graphisoft.com/t5/GDL/Dynamic-Polyline-base-code-object-VERSION-2/m-p/249973#M4455

Hi John. Here is something to start with. New verts are created by moving the hotspot in the circle.

I have wondered that, too. Try to draw 3d elements in the right place. If You later move them they possibly remember their original coordinates. That is my impression.

Maybe curves are too detailed. You can reduce any polyline in QGIS and export to dxf.. It´s free and it is very useful for landscape architects.