I have no issues with ISO at the high 13’s. I’m not a physicist but the vapor pressure should relatively increase at altitude right? Cold is what slows them down and I regularly use a windscreen around the can, accepting the risk of blowing myself up. Hasn’t happened though.
This is right. I have had the same experience as Shooter71 and occasionally over 14,000'.
When heating water for just myself, I use an Optimus Crux with a 32oz. Halulite pot made by GSI. It will heat about 24 oz. of water.
When heating water for a small group I use an MSR Pocket Rocket and an Olicamp heat exchange pot. It will heat a full quart.
The Olicamp pot is a little too big to fit properly on a Crux stove. Or maybe the stove is too small