For what it is worth, mine is set at 63 and it allocates the remaining 192MB as system RAM.
I wonder if it might be the monitor setup in devs/monitors or perhaps your P96 custom screen modes. My A4000 is under a table at the moment. When I reconnect it I can email you my monitor driver and check my P96 preferences. I don't know about you, but I had to build each and every P96 screen mode from scratch (doesn't take long once you've worked out what your display can handle).
