Well... I guess no point figuring out what part of the chart would be Zi, as in here Jupiter and Sun are in the lowest middle part, where Zi is in Lo Shu.
And both so close together on that day in that part of the chart can't be a coincidence, so I think we can accept this was what the year pillar was originally based on.
However, if we look at it carefully we can see they aren't on top of each other. Jupiter has drifted way off almost moved to where would be Gen Trigram in later heaven...
I would guess that is either because the sidereal period of Jupiter is less then 12 years as already mention(exact number is Jupiter: 11.86177556 from here btw:
http://www.skyscript.co.uk/mean_conjunctions.html, although it seems unlikely as it would drift much, much more if it was that)
Or because they actually did use tropical view and didn't account for the precession. We use fixed degrees to align both charts now, so it doesn't look like a big difference, but its a lot for 4 thousand years and would it would need very different corrections.
In any case, Jupiter seems to be drifting away, Moon doesn't fit perfectly too.
Still too close, to be a coincidence thousand of years after the calendar started...
So I would think of it that way. First possible development. They did made it based on that. However, they didn't knew enough to made it accurate enough to be able to continue for so long. Second possible development. They made it based on something too complicated to explain at the time(much like QMDJ or ZWDS), and presented this so its more widely accepted. Then just align a date to a conjunction that they knew was going to drift off, while the calendar itself calculated something else behind it that wouldn't.
I like second one more.
So at the same time somewhere behind it all there is some 12 /10 year relation that fits perfectly to what is calculated. Be that sunspot activity or whatever, someday we will find out I believe. But it can't be this, this is already drifting of in both sidereal and tropical way of viewing it.
I do believe we will find out with time, though. I've worked with many systems that use random info, they can never be so accurate. So there is another reason behind it all and as I said I can believe in the idea that maybe the people that created the calendar knew, while they presented it for astronomy relation for everyone else and made it start from there so it fits at first glance.
So while fixing the relation to something else, they could have said Jupiter <>Sun <> Moon was the reason and was actually aligning it to something much more primal and important that we currently may not know(though I can guess, but much, much more testing will be needed in the future in very different fields).
Anyway, thanks to everyone this was useful in many ways.
And I know a lot of its parts we "agreed to disagreed" with, much like the month branch inversion. But its all good, it was interesting and useful topic in my view. : )