Do you really use the newest version of Mp3tag?
I don't see any "Parameter" field in my action "Export cover to file"
This action creates the absolute path C:\cover art if it doesn't yet exist. Then it creates a subdirectory with the name of the artist inside C:\cover art. And inside this artist, it creates an subdirectory with the name of the album.
Be aware that this only works if your artist- and album name doesn't include any forbidden characters like * or ? or / and some more.