I've read further into this, and it seems we could consider Divisional Field Hospitals into OOB after all.
As medical organizations gained experience of how to operate most efficiently, they decided to divide these Field Hospitals into two sub-organisations, as it became evident early access to surgery was a key factor in saving lives.
Field Hospital / A was operating nearer the front lines, had 50 beds, and was responsible for urgent surgical operations, that should not be postponed.
Field Hospital / B was operating further from the front lines, and was where the recovering patients and less severely wounded were recovering. It had 150 beds.
Based on this, we could consider these Field Hospital / A -type of fixed locations to be a part of the game scale?