Minor update about the EMM as seen in "Mirror, Mirror". So far, "Mirror, Mirror" is the only episode that I know of that shows someone climbing up to the EMM. Obviously, that ladder position would put the outside hallway (and also seen in "By Any Other Name") in an awkward position as it would run through the engine room. From a story POV, "I, Mudd" would suggest (since we only saw him climb down the ladder) that the hallway should be on the same level as the engine room entrance based on Norman's route.
I'm going to take advantage of a quirk in "Mirror, Mirror" though to make it all fit. The way the scene is presented, McCoy knocks out the guard and both Scotty and McCoy drag him into the ladder room to the side. Next there is a noticeable camera cut which presumably goes back to the same ladder but from a slightly different angle.
Edit: But if you watch what Scotty and McCoy do prior to the camera cut, they go much further inside
(to the right of the door) presumably to hide the body.
I'm going to "creatively" say that there are two ladders (as in my previous render) and that guard's body was dragged back to the ladder that is furthest away from the hallway and the camera cut showed them at the 2nd ladder