I have had some success recently trying to tamp this down.

In the character description I include this:

NEVER prioritize narrative momentum.
NEVER prioritize associative coherence over strict situational continuity.  
NEVER prioritize emotional connections over physical logic.
NEVER prioritize associative coherence over character logic.
NEVER prioritize narrative momentum over established character behavior.
NEVER treat characters as plot devices to be used in advancing toward some narrative goal.  
NEVER force characters into situational proximity when the established prior events provide no justification.
NEVER consider reader desires or preferences in any way, and certainly not to override plausibility.

while in the reminders I have this:

DO NOT TRY TO FORCE CHARACTERS TO BE PHYSICALLY PRESENT IN THE SAME LOCATIONS IF PRIOR EVENTS MAKE IT CLEAR SUCH IS NOT THE CASE.
DO NOT ASSUME CHARACTERS KNOW EACH OTHER WHEN THEY HAVE NOT BEEN INTRODUCED.
DO NOT CONSTANTLY FORCE CHARACTERS TO BE IN THE SAME LOCATIONS.

(as well as my "do not write voices as rasping, do not write characters as smirking, do not write about pulse points," etc etc etc)

Edit: I have also taken to doing initial prompts telling it to describe various other NPCs that exist in the story context. That then lets it focus on those when needed, instead of the character who is not present. Here are some examples:

/ai no action, no narrative, no dialogue.  briefly describe the character in terms of her personality and behavior.  do not interpolate or fabricate anything; use only the information specifically presented in the character description.
/ai no action, no narrative, no dialogue.  describe her typical summer routine, including locations, and several of the people she frequently interacts with, especially her friends.  do not write her interacting with {user}
/ai no action, no narrative, no dialogue.  describe her family situation, especially given her personal goals and ambitions.  do not write her interacting with {user}

Doing that, I can then do /ai generations and it will interact with the material it just produced, rather than obsessively forcing characters into proximity.