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It's not so much that a larger tank is needed, but a larger surface area to evaporate gas off the liquid propane in the tank. This larger surface area is found in... larger tanks. But if they made a 1lb tank like a pancake you'd be fine.
I've never had a problem with mine either.....No matter the elevation or what size tank is feeding it !!
I take my portable buddy with me every other year to Arizona, Flagstaff area 7000 feet, no issues. I feed it from 1 lb cans and 20lb cylinder. I live at 900 feet and use it all winter as well here.Never had a problem with any 1lb cans at any altitude, have been up to 10,000ft camping. No issues with heater, lanterns, stoves.