Why won’t my MSR Pocket Rocket Deluxe ignitor work at 12000 feet?

I just used my new MSR Pocket Rocket Deluxe over the last 8 days at elevations from 10,300′ to 11,900′ and found that when I had the pot on the stove, it would light on the first try but without the pot on it, it would not light using the piezo. At home around 5,000′ altitude it will light up first try with or without a pot on it.

I guess the pot changed the air flow and the mixing somewhat. Seems reasonable.

Cheers