I feel it has to have some kind of internal logic beyond 'it's on the screen, either it's there and we have to make every single engineering decision based on that one shot or we have a holographic projector there'.
Frankly, I wouldn't mind if it were possible to shift the intermix shaft all the way to the stern to the point where it matches the center of the yellow circle at the bottom of the TOS Enterprise
because that's where I placed Reactor 3 in my TOS Enterprise
deck plan project here at the BBS, so I'd welcome the FP blue corridor extension.
However, we have to deal with the forward and aft torpedo bay from TWOK and therefore, IMO, the spacing between the turbo shaft (presumably between the forward torpedo launchers) and the continuing intermix shaft (presumably behind these "back walls" of both torpedo bays) would somehow have to match the distance between the intermix shaft on the main engine room level and a turboshaft somewhere near the blue corridor.
I'm mostly concerned that the blue corridor with
the FP extension shifts the intermix shaft beyond torpedo section docking port. As a result, the intermix shaft would have to run through the center of the aft torpedo launcher (Torpedo Bay Section 4), which it apparently does not in TWOK.
I agree that he ship has to have internal logic which always brings me back to the turbo shaft system. The TWOK torpedo bay extends so much to the bow that the remaining turbo shaft space and/or location is limited to the narrow bow of the connecting dorsal.
Thus, on the upper level of the engine room Kirk first showed up in TMP either the blue corridor is shorter (because the FP extension is a fake display) to make space for a central turbo shaft or
the blue corridor is leaning towards the starboard side enough to have a turboshaft in the center axis / horizontal intermix shaft alignment. The original studio set plans
could suggest that, but then - why were Kirk and Scotty running towards the starboard side
If the turbo lifts are exclusively located to the port side and the "whole" blue corridor is separating these from the other side, there couldn't have been a turbo lift cab there to get them to the transporter room which apparently was located in the saucer.