Pitboss issue

Ok I have a linux machine that is my router/firewall/pitboss/<lots of other stuff> machhine.

I can connect to it fine and play my turn. My friend outside my network can also do so.

But we can not both log in at the same time. It gives a message about not being able to contact peer.

Here's the network:

Friend - <internet> - PitBoss Server - Me

Now, if I'm away from home, or tethered to my phone, we can both be in at once. Then it looks like this:

Friend - <internet> - PitBoss
Me /

So . . . what do I need to do to make it so that we can both be logged in at once in the first scenario above?