How do I make the Level Editor prefer my FC directory?

[Your Computer]

About changing the editor's default folder for static objects, you gotta edit the file redist/MainEditorSettings.cfg
You'll know what to do when you see its content.
It should solve your grass placement problem.

btw, this works too if you want the machine for pigs models listed in static objets instead of ATDD.

The reason why i didn't mention that is because it'll create another, worse problem in the process: you'll lose direct, menu access to the original assets.