Now that I see it in actual use as opposed to a catalog photo, I'm not sure that this particular dual-capsule mounting accessory (I realize that it's Neumann's) is optimally designed for M/S recording with an AK 20 capsule.
The two microphones' diaphragms should be at the same distance from the center of the direct sound sources, but from the photo, it looks as if the figure-8 microphone's diaphragm is about 1/4" to 1/2" ahead of the cardioid's. The two diaphragms are perpendicular to one another, so this is a matter of getting their center lines to line up. The AK 40's diaphragm is just slightly behind its front screen, i.e. about even with the top of the printed markings that are on the circumference of the capsule. But the AK 20's diaphragm is centered within the slots in the grille, no? (It should be visible if you shine a flashlight through the capsule head.)
The AK 20 capsule is taller/longer than all the others in the series not only because of the capsule's internal orientation, but also because there's a rotating swivel joint between the barrel that contains the FET, etc., and the capsule head itself. It looks as if the designers of this dual-capsule mount didn't take that difference into account.
--best regards