Hmm, something to think about.
Hacksaw is right about the breakdown voltage - simple physics. But that could lead to early discharge of the spark energy somewhere far away from the regular ignition spot (probably inside of the piezo module?). I do had ignition problem with my favorite piezo-turbo lighter at high altitude. No matter how the gas pressure wheel was set - just no spark over the jet opening... But I thought that's because of a high humidity in that place...