scene is actually filmed in McCoy's Office next door, and the flat panel is simply adjacent to door (on one side) and Spock's bed (on the other). This set plan should explain better:
(click for full size)
Just got back from the holidays (had the chance to embark on a 1960's Soviet Juliett-Class sub).
You are right, the flat panel is on the wall where you put it (I do not remember having really seen during TOS).
But in many shots taken in McCoy's office we do see the exam room to the right through the door frame and I wonder, if this flat panel wall shouldn't usually be in the way?
Season 3 is the worst offender though, IMO. Some directors (Truth...Beauty) seemed determined to present the adjoining Sickbay rooms as completely separate!
You make it sound like you feel it's a bad thing.
The more I think about it, I wonder if the Enterprise
should have medical space that's not only limited to the crew. The ship is often on patrol duty and provides medical assistance to colonies and outposts, and it has at least 4 "astro-medicine medical wards".
I'm currently taking notes of all the sickbay variations and probably present a "sickbay studio set sheet" with the variations and corridors presented during TOS to illustrate the issue (I will need to correct the studio set piece you featured, McCoy's office wall shelves aren't nearly as sunk-in as the "official" studio set plan sugests).