I would expect it to make a bigger difference at low power settings, so I don't think it's confirmation bias at all. 10 seconds of almost-high output compared t

I would expect it to make a bigger difference at low power settings, so I don't think it's confirmation bias at all. 10 seconds of almost-high output compared to 9 seconds of high output won't see much difference. However, 10 seconds of low output vs 2 seconds of high will see a big difference. Same amount of energy, but delivered over a 5x longer time period.