Core memory and OS/8

One of the reasons I bought Vince's 32K SRAM board for my 8/A is because I was having flakiness with my "real" core boards (two 16K and one 8K). Now that OS/8 is running again, and my RL8A and two RL02's are as debugged as they're going to get, I decided to experiment with the old core. Put them back in the chassis and... the two 16K boards are now working perfectly. I ran it for two long passes with DHKMAD (checkerboard diagnostic) with no errors! What's strange, though, is that OS/8 won't boot unless both 16K boards are in the backplane. Then it does boot and a MEM shows "32K MEMORY!" as expected. Won't boot with 16K or 24K of boards, either. I thought that only 12K was mandatory (at least that's what the Device Extensions manual says for an RL01). Or is that something that's set up during BUILD?... I don't see anything in the OS/8 manual and I know I had OS/8 running with 16K and 24K previously. -Charles