Jack Black:

I DO have a CIH 1200 (12 row stacker) and I had the same problem as you for a while.

I just about went crazy...my story sounded a whole lot like yours'.  I got some relief (it evened out w/the other rows) but tweaking my singulator quite a bit.  I can't remember the exact number now, but it seems like the other rows were on "3", and this one came close to being equal at "5" (or something like that...maybe it was "1", but I do remember that there were a couple of digits between the other rows and this one).  Like I said, it was better, but still not exact.  I like to have my planter perfect (!), and it sounds like you do, too.

I kept on & on tweaking it, 'til one day I took the vacuum hose off, and got to where I could see through it completely.  Sure enough, where to hoses met (seems like the coupler on the hoses) there was an obstruction.  The obstruction was not complete (i.e.: there was obviously enough vacuum getting to the row to make it work somewhat), but it was enough to lower that row's population.  After doing this, I was able to reset the singulator to the same as the other rows.

You might also try changing the box to a different row, and see what it shows..

I hope that is what your problemo is.  I love love love my CIH 1200 planter.  It has things on it that all planters should have. The planter before this one (for me) was a JD MaxEmerge, and I could not stand the way the depth control wheels (just outside the d.disc openers) on a JD "pushed", instead of "pulled" (like they do on our 1200's).  I also like how one disc opener is slightly larger than the other. 
BUT

CIH had some crappy quality control personel doing the final inspection!  I had tons of chains that did not have the keeper(s) on the master link(s).  Also, the monitor wiring going down to the drive wheel was touching the chain, and would not have lasted 'til the water got hot !! (I have a ground-driven planter, not a hyd. driven)

To fix my wiring near the drive wheel/chain, I JB Welded a 1" piece of hard, 1/2" pipe to the arm, and ran the wiring through the pipe; thereby keeping it away from the chain that would have eaten it in two...

Let me know if I can help you any more, and hope this and the other ideas work!