Why do I have to keep on changing my fit? I realize there may not be a true "answer" to this, and some of what I have to say makes no sense, but since I'm not exactly the brightest tool in the refrigerator, it may just be that there is something obvious that I'm overlooking.  I have this O/C thing about constantly adjusting my bike fit (which seems to get worse as the years go by).

No matter how I adjust it, it always feels like something is not right.
There were over a 1,000 changes since 2008, in the last 5 years averaging over 120 changes per year. I've had 6 bike fittings — every one left me LESS comfortable, and slower — with such a variety in positioning, that you'd swear they were for 6 different cyclists!  For example, one had a saddle-to-bar reach of 52 cm, another 59 cm!  So, I know I won't find an answer there. 

The main issue seems to be that I need to keep changing my position in order to stay in the same (relative) position.
Here's what I mean:  With all my "fit fooling," I've determined the most efficient (and comfortable) saddle position is pretty much "heel-on-pedal" for height, and "knee-over-pedal-spindle" for setback, give or take a few mm.  (I actually use the "hands-off"/"balance" test to set that, but that also puts me KOPS, so I just call it that.) The thing is, some days I can pass the hands-off test with the saddle tip 8.5cm behind BB, other days I can't pass it unless the saddle tip is 10cm back.

Likewise, some days a saddle height of 79 cm (BB — center of saddle) is HOP, other days it 80cm.  (And, yes, I'm using the same bike, pedals, saddle, etc.)  Usually, soon after I start a ride, I'm like, "WHAT THE &amp;@%*!?!?!?!", because the position feels so screwed up, it's like I'm on someone else's bike!  (Even though the day before, the fit felt perfect.)

So, I spend most of the ride adjusting things, then — usually a mile or two before the end — I finally get it just right.  Then, next ride, once again it's "WHAT THE @^#*?!?!?!?!" So, the whole process starts again. (Like a cross between "Breaking Away" and "Groundhog Day.")  I also fool with the bar position some, but not nearly as much as the saddle. The only theory I came up with — that my job had something to do with it — didn't pan out. (I'm a mailman who walks 8+ miles a day up and down God-only-knows how many hills and steps).

I was thinking I might need a different position when doing a ride after work than when riding on my day off.  Experimented for a while with that, but didn't discover any pattern.

I suppose fitness/fatigue levels may have some affect, but could that result in "to my problem", but wouldn't such big difference in height and fore/aft on a daily basis indicate something PHYSICAL is going on?  

If I didn't know better, I'd think my legs randomly grow and shrink at will, or something! Is it possible that I just need a different position on different days?  Could it be due to my torso being 10-11cm shorter than normal compared to my legs? Any suggestions appreciated, but, again, I understand if it does not have a clear answer.
Often, I get on my bike and things feel a little off. I put it down to varying fatigue, stiffness, amount of sleep, mood, stress or a hundred other things. I then try to get get warmed up, then concentrate on good technique and having fun, or, if I really am feeling off, cruising along for a bit then getting a coffee.

It sounds like you have trained yourself to be hypersensitive to feeling 'off', then feel the need to need to mess with the saddle position. Maybe you just are not letting you body actually get used to an reasonably OK position. What you need to do is get the position ballpark right, then just stick with it and let your body get used to and adapt to it. I also wonder if regular stretching would make you feel better on the bike.

I'm not surprised that different fits came up with different positions. Bike fittings are not supposed to find your 'perfect position' - that does not exist. They find a good position for a particular purpose. Different fitters may have had a different idea of what you were trying to achieve. Also, I'm not surprised you were slower after each fitting. Your body was not used to the new position and hence you could produce less poswer.