"Can you illustrate out how you arrived at this? I've watched that episode many times but the only information I can tell was from the signage that put him near the hangar. (BTW, I'm not using a tighter circular corridor around the yellow circle.)"
I'm currently working on schematics for the engineering hull but given my lack of CAD skills I will have to resort to traditional techniques using the Franz Joseph blueprints as a background on which to overlay the actual and "tweaked" studio set plans.
I don't think that Decker necessarily arrived "near" the hangar. He merely arrived on the H(angar) deck level (deck 13 according to your cutaway) and that sign near the ladder could simply be a deck marker that tells people on which deck they are.
Nevertheless I believe he arrived at a (semi-)circular corridor near the yellow circle which corresponds to the circular corridor of deck 12 above (Kirk's provisional quarters in "Mudd's Women") and further up the one leading to the "Engineering Section" ("Ultimate Computer", "Journey to Babel"), above which there is the corridor next to the Auxilary Control Room (deck 8) and the ladder down to the upper level of the Engineering Section ("Doomsday Machine"), although Scotty and his enginners seem to have taken a detour through the other rooms on the starboard side upper level.
The general problem with the external windows in Kirk's (and Mudd's) quarters simply is that the only feasible explanation is to have these in the engineering hull next to a circular corridor (or a piece of it). Same with "Mark of Gideon", it's a curved outer wall that could only be in the engineering hull or the 'teardrop'. But even in the 'teardrop' (did they recreate the entire ship or just the saucer?) there would have to a tighter circular corridor.