Cockie and granama, if I have it right (which is always a big if!) the “origin” of the ideal MD is a physical state taking in 3 entries in row 7. I think that Buddhists might be the most inclined to regard this as “the origin of the ideal MD”.
Meanwhile, I have just cracked the secret barred off cells. D’oh!! “Up and under” as whatsisname used to say!
Many thanks, Penumbra. You gave me a bit of a runaround and then a chuckle. The marks of an excellent puzzle.