Unfortunately it doen't work properly... there are tags to support it but they seem to be broken.
You can get it to work... but you have to implement a workaround.... have improvement produce a (local) resource then make the unit require the local resource to be constructed. It works but it's not ideal.
If you search you should be able to find some more info on how to do it. If you can't get it going post back and we can give you an example.
