I knew there was a tip-over sensor that shut the heater off, but there's also an oxygen depletion sensor. Not only does it shut off the heater when oxygen levels get too low, the sensor means the heater isn't designed to function properly over 7,000 feet elevation. I'm camped at 7,596 feet right now.
So, if you're cold because you're at higher elevations, too bad? It would be nice if the sensor also sensed elevation so it could compensate.
However, the heater worked okay when I was camped at about 8,500 feet in northern Nevada. So go figure. Maybe Nevada air is denser. Or it's just that the heater elves are messing with me. Solution: go where it's warmer.