It took awhile, but I think the following "Rest of The Story" on this type of director - and Texas' units, in particular - finally cleared up some major confusion:
Click on Image to Enlarge
Other views (also admittedly of very low-resolution) look even more different. At middle-left, the side wall (of Texas' aft Mk50 on 10/27/45) looks to be truly flat. And at middle-right (from the same archive pic), only the top half of her forward Mk50's side wall appears flat, while lower down it does appear to revert to the original, cylindrical shape. However the upper half also appears to fair-into a large, squarish slab at the back, which rises to form the highest (aft-most) step in the roof. The net effect - resembling nothing so much as the Mk50 wearing a large backpack - is also 100% consistent with the earlier back-side view (top-right), taken of the same unit just 3 weeks prior.
At bottom-left, a "backpack" is also apparent on New York's aft Mk50 (photographed 11/14/44) - though in this case not appearing to be faired-in, as above. And at bottom-right, Texas' aft Mk50 is seen (on 2/3/45) again with a "backpack" only half-faired-in, at the top.
A subsequently-discovered reference - a beautiful pic of Texas in shiny new 5N paint, taken 1/6/45 - finally shed light on the above, and even suggests the function of these "backpacks":
Click on Image for FULL-RES
Such a soft back wall of the Mk50 cab is easily understood as a protective feature: weakening the back of the "tin can" to permit any blast pressure and/or ricocetting bullets/splinters to exit asap. Also, such large openings and replacement of considerable steel with canvass would serve to greatly reduce the heat in these sun-baked postions, highly exposed. Canvas (or similar tarp-like) covers also can explain the occasional appearance of partially- or completely-flat sides, as well as other variations in appearance documented.
By now I have also found two more pics, further revealing details of the back sides:
Click on Image to Enlarge
At right, the closest-yet glimpse (of Texas' aft Mk50 in February, '45) is maddeningly obscured by the mainmast and a radar grille - both masked-out (red) in the inset, for clearest interpretation. Again, the back is clearly flat-sided, the double-doors visible - and (at least one) now open - in a section of lighter color/texture (i.e., presumably canvas), comprising about 80% of the back side. At the top is a (darker) section appearing (despite the obstructing radar grid) to be horizontally striated - if not accordion-pleated, outright - precisely where the canvas back must furl/roll up onto. Whether the double-doors might also have been collapsible - canvas stretched between, for example, telescoping doorjambs - is unknown, however one can also imagine they could easily have folded down onto the deck - or upward into the overhead - when the back was raised.
In any case, it is clear that from perhaps very early-on, Mk50 Directors - and certainly those on Texas - were fitted with these "backpack" modifications to the (presumably original) "tin can" design shown in the Navy manual, above.
If any of you out there has further pics/info you can add to this, (where the hell were you a month ago , and) do pipe up with it!