Ignition timing on NX50

[vintagegarage]

I'm trying to figure out the ignition timing on my NX50 Express SR. Specifically, what is the pulse generator looking for while the flywheel is spinning around it? The inside rim of the flywheel has 4 permanent magnet segments that all look to be identical. The pulse generator is positioned such that it might be looking for something on the inside rim of the flywheel, or something on the central raised threaded boss on the flywheel. I can't find anything on the inside rim of the flywheel that is specific to a single position, and if the pulse generator is looking for the permanent magnets, I would think it would fire four times per revolution of the crankshaft. The only thing that seems positional on the threaded boss is the keyway cut into it. It doesn't seem possible to me that the pulse generator is able to sense the keyway slot in the central boss, so I am baffled. I have two different stator plates both with pulse generators, and they both test to be identical on the bench, but they have slightly different ignition timings. One fires slightly in advance of top dead center at idle sometimes stopping the engine with a thud, but its advanced timing allows the engine to start on the electric starter. When I use the kickstarter with that one installed, sometimes the spark plug fires before top dead center, resulting in a kickback. The engine runs ok on the second one, but it will only start on the kick starter, and is very difficult to start. I think there is too much retard in the second one. I theory, the timing is not adjustable, but the stator plate has slightly slotted holes, allowing for some rotation when mounting it in the cap, but the slight variation in position doesn't seem to affect the timing. I clearly don't understand how this works.

Does anyone on the forum understand how the CDI knows when to fire the spark plug?