he did several times ^_^. people just keep asking him the same question so it takes longer.
He never answers the question directly though. Only that "he eliminated every other factor other than the drivers themselves", what that means is entirely up to his, your and my interpretation.
To me, it means that he unplugged the L / R driver, swapped it around, then put it back into his "unprofessional measuring tool" and ran the "measurements" again. Then getting the result that is similar but reversed for the L / R channel.
That is of course, not helpful for diagnosing the problem if he has recently grown a brain tumor that is compressing on his auditory nerves. You see, he'll need to swap the drivers, then stick it in his ears and see if he can detect the channel mismatch. For the purpose of discussion say if originally the L side was softer, after the swap, the R side became softer. However if after the swap the L side was still softer, that means he'll need to get a medical examination done, there are medical conditions that can cause mismatched hearing and doctors actually check for this as an early sign for several medical problems.
Of course, best to do a single blinded test and have a friend / family member do the driver swapping without his knowledge and see if he is still able to identify the softer / louder side correctly about 10/10 times.
If he is able to pass the single blinded test, and it still bothers him, the only solution left is - play the low frequency matched channel matched lottery game, or find a custom IEM maker that will tune the channels to the level of matching he desires.
Regardless, my point is that +/- 1.5 db mismatch under 100 Hz is not a legitimate concern for just about everyone out there. I myself have a hard time distinguishing +/- 0.5db at 440 Hz using a very sensitive volume changing sine tone ABX test. Doing this same thing more than 3 octaves lower at 50 Hz is unthinkable, especially without a level change, and just detecting it casually after plugging into the ears.
P/S: I legit missed JohnYang's post that also suspected his hearing instead of the drivers.