I sure as hell wouldn’t know why. But I do have a question…
So what does “better” mean? Are you comparing to the original pre-compressed audio? The lossless should sound exactly the same, otherwise it ain’t lossless.
Now if “better” means something other than faithful to the original, then maybe the audio processed by the lossy encoding has a perceptually useful effect.
When I think of testing these kind of perceptual options, I think it should be as we would with Monster Cable or something like that. It should be blind (or Stan Lipshitz would insist double blind) and it should be AB testing not ABX. And half the time A and B should be identical sounds, which is what keeps the test subjects honest.
So you hear sound A and you hear sound B. You can even repeat hearing sound A and sound B. Then the only question that the test subject has to answer is: “Are these two sounds identical? Or are they different?” It’s a yes or no answer, and the answer is either correct or incorrect.
We subtract the number of false positives from the number of true positives and we subtract the number of false negatives from the number of true negatives and report those two numbers for each test subject. If these two differences are a decent positive number (in proportion to the number of test sounds), then it can be inferred that this subject can accurately hear the difference when there is a difference.
But objectively testing for “sounds better” becomes a much more difficult thing. What’s “better” for you might not be what sounds better to me. I dunno.