Has anyone else tried playing as Poland after unlocking them using HussarTW's excellent startpos mod?

I've had several attempts now but can't secure their position and keep them alive. Within a short period Prussia will allways attack you and overwhelm you with sheer numbers. I can win several battles but inevitably even constant victories will cost me some men and result in a slow attritiony doom. Has anyone managed to get them to work? It seems inevitable that you will lose.

Also, is Prussia hard coded to expand into small nations rather than large ones? They allways seem to attack protectorates.