What they said. Correct spacing is important.
Of course many people deviate from the Jecklin standard, personally I prefer a bit wider spacing for more separation at lower frequencies but that becomes difficult because you either need to get closer to the source or use a larger diameter disk to keep the same angle between the edge of the baffle and the mics. From what I've read, it seems Mr. Jecklin modified his technique latter in a similar way (spaing approx. 15" with a 15" in disk if I remember right). Going the other way, Moke's mini-jecklins need the mics closer to the surface for effective baffling given the small size of the baffle.
I've thought of using two small disks and spacing the disks apart to increase the low end separation to avoid needing a Kimber ISO-phone size monster disk. Idea being to keep the angles right and the mic to disk space small enough to be effective with a small disk. Just another untried wacky idea for now - baffled A-B, I guess.