[Andrew9999]

So I installed Microsoft Message Analyzer and monitored the traffic between PC and tablet with a direct connection active.  It's true the remote end point is connected via port 48000, but the local end point (the master) uses port 51854.  When I forwarded BOTH TCP ports everything worked.  In fact the page turns are as instant as when the tablet is connected via local wifi.  Hurrah!  

Note - the Fritz!Box warned me that I could only have one port (or range) forwarded to a particular device at a time, but accepted the addition of a second in any case.