That actually confused me a little because, while it's accurate to the actual set, in the movie Kirk uses the magic of editing to walk in from a corridor to the upper level of engineering (in both movies, actually), but there's no exit from the upper level.
It's less clear in TWOK, maybe a new entrance was fitted in between the movies? Perhaps even one of the single-person lifts?
However, for TMP when kirk enters the Engine Room from a long straight corridor and through an entrance foyer, I am still sticking to my suggestion from this thread from a few years back:
https://www.trekbbs.com/threads/blssdwlfs-tos-enterprise-wip.119751/post-8905828
The scenario is that Kirk is trying to find a quiet spot to break the bad news to Decker:
1) Kirk arrives at the upper level and peers over the railing. He spots Decker and takes the starboard-fore lift down to the main level.
2) Something (or someone!) catches his eye on the lower level and he pauses to gaze over the railing for moment. He then realises that in the meantime Decker has taken the port-aft lift to the upper level!
3) Since the upper level is a nice quiet spot to speak privately to Decker, Kirk takes the starboard-fore lift up to join him. However, Decker was only up there to collect a report from an underling and has now rejoined Scotty on the main level. Kirk sees this shortly after stepping off the lift and moving to the railing.
4) This puts Kirk's back up a bit - Decker couldn't possibly be avoiding him on purpose, could he? Kirk walks smartly to the port-aft lift and rides it down, no doubt cursing the absurdly slow speed of the lifts and wondering if a ladder could be fitted somewhere instead.
5) Kirk does not take his eye off Decker this time until he finally gets to speak to him.
It's a bit of an absurd scenario, but then it's an absurd camera shot too. However, it might explain Kirk's extra abruptness when dealing with Decker, whose cheery attitude would merely fuel suspicions in Kirk's mind that the young captain was leading him a merry dance on purpose. Kirk's terse "let's talk" before leading Decker over the FOYER of all places to publicly demote him would naturally follow; Kirk would have preferred somewhere private to do this, but he's wasted enough time chasing Decker around Engineering already!


