I am sitting in the room I have set (for the moment! temporarily!) aside for laying out the fortress.
Looking carefully at it, it came to me that if I were to complete the circuit of the walls, I would have a pentagonal fortress of five bastions on my hands. Perhaps this could be a future project - I would need another two bastions and two lengths of wall. What's that? A week and-a-half's work? The two half-bastions I have go together reasonably neatly. Not perfectly, but not too badly.
The next thought that came to me was that it would be immensely cool to complete that circuit, and set the fortress up on a table with a hatch in the middle and be able to poke my head through it (a la Peter Young) and survey the field from within my fastness.