Sean, that makes sense to me, but clearly was not the design in these cameras, as countless photos of them, and users, attest. My only guess is that unlocking might have been considered a bit too jarring, or a low position of the small cam lever inconvenient.
Maris, you certainly know the cameras better than I. Mine has no serial number -- anywhere -- for whatever reason, as attested also by the repairman. I have seen photos of some that did not have toggle cams, some with apparently fewer movements.
In any case, the maximum room I have for washers is about two 0.5 and perhaps one 0.1, before I'm no longer able to align the horizontal holding screw with the hole in the vertical post. As I said above, I've tried various combinations. for a while until recently, two 0.2-mm washers on each side seemed to be the ticket; now just one seems to be best, lowering the camera lever position at closed as shown immediately above. These thin washers do indeed get bent. The internal diameter is 5 mm, outer is 7, though in my pack of 0.1, 0.2, and 0.5 from Japan (called stainless steel shims) there appears to be some slight variation in the width of the band. The contact surface of cam to washer is indeed quite small, and both surfaces are polished quite smooth.
The only other thing I can think to note, is that the thinner, outer part of the steel guide rail, not being screwed down to the bed like the inner length, bends just slightly up if slight forward pressure is applied to the front standard, making a faint click when it comes back down on the bed, even when the cam is closed. This simply allows a tiny bit of play in the front standard, though it has not effect on operation normally (i.e., without aiming the camera severely down as I did recently).
Probably there isn't much else to explore here. These are hardly calibrated Sinar P mechanisms (which would not make my photography any better), and wear and tear by inexperienced or rough users, which my camera seems to have experienced long before arriving in my hands at an unusually low price, may have been enough to push several factors minimally out of original spec, just enough to make the difference.
Again, I am grateful for all the help.
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