It depends.
I think a better question would be: by what mechanism could a premium IEM sound better?
We got frequency response measurements, we can look at distortion and we all have the ability to EQ bass and treble to taste.
This would have to be done, regardless of the price of the IEMs, as people have different preferences.
For the top end I'd experiment with shelf filters before trying individual filters and luckily all of this can be ABX'ed quite easily.
This leaves the wildcards: comfort, seal, fit and insertion depth.
Why would a more expensive IEM fit better other then random chance unless they make a mold specifically for our ears?
Perhaps I am behind the times and I missing something, but that is all I know.
This is not to discredit any positive experience with more expensive IEMs and I very happy to hear you are all enjoying what you have.