those are different contexts. with abx we have a clear reference to get back to. when we purchase a headphone with 1dB imbalance(usually not everywhere in the frequency range, but also usually reaching more than 1dB imbalance somewhere), we have no reference. we just listen to that headphone and unless the difference clearly generates the feeling that something is wrong, we're likely to just enjoy our headphone like anybody else. and it's a good thing, because otherwise we'd have to throw most headphones and IEMs ever manufactured to the garbage. ^_^ I also feel 0.2dB clearly in direct comparison(in the midrange!), but just as well I will often forget my EQ on the wrong position or set for the wrong headphone and spend sometimes a full day before noticing. just enjoying my music as usual. when discussing perception here, we have to be clear about the testing conditions because the result can massively depend on them.