Google is not the answer to everything.
Internet search does not supersede empirical. Your "tent experience" has clouded your mind . Run a bloom room with your dual port, then replace it with a mini split/5 ton. Report back with 20lb tank duration for each. Even then, at this point, I would doubt the "credibility" of your findings. Not because I believe you to be dubious, but your general knowledge/experience appears to be lacking.
This isn't just my own experience, but that of every grower I have ever known that tried to use a portable in a bloom room. Low wattage, a light or two, it may not be as noticeable. Less heat generated, less operation, less CO2 "extraction". However, it will still be "stealing" CO2.
Whether you are open to the facts, or not, portables, single and dual port, suck CO2 from the room.