Be interesting to find out. We have become top Tetris players fitting stuff into tiny rooms.
We have regretted it sometimes when trying to do a service.
The only time we have ever refused was when the reclining chair didn't have room to recline.
We don't have a specific minimum but, I go on the home assessments and want to see sufficient room to recline a chair and have a paramedic work on the patient. I also want to be sure that there is enough room to perform a service and or escape the room in the event of electrocution, not for my benefit, but I'm sure one of my Techs would need that ability.