Sorry - I should have been clearer. Yes what you are seeing is what I anticipated. Setting the TMPDIR in that location is only for the dashboard, which is lower in the stack than Passenger. In any case, I thought the RackMultipartNAME are the real culprit for blowing up any drive, and so was focusing on that.
For the other settings/other temporary passenger things, maybe you’re looking for this or at least I’d search that page for tmp to indicate how you can migrate everything off of that directory.
https://www.phusionpassenger.com/library/config/nginx/reference/#passenger_instance_registry_dir