This has bugged me for year, but I finally opened it in Transmission a couple of weeks ago.
I use an Apple Airport router and it was just a simple matter of forwarding the torrenting port (I use the default 6881) to the 6881 port at my local IP address (10.0.1.7). Ticking "Automatically map port" seemed to be a good idea as well.
That interface for your router seems a bit confusing, but all I can suggest is that you put the same port number into all of the holes in that form, as well as in Transmission.
Sorry I couldn't be of more help!
//doobi18