Didn't feel like posting in the firestorm, but it looks like things have calmed down. My knowledge of how headphones should sound is significantly better than my understanding of IEMs. In my review, I had attributed the supposed dip to a soundstage difference in headphones and IEMs.
"Because it can’t all be rainbows and kittens. It should be expected, but even higher end IEMs have a lacking soundstage when compared to open headphones. Orchestral recordings I enjoy greatly on headphones did very little for me on the 4.Ai. I’ve also noticed that the “richness” of a song is not always there."
The 4.Ai really sparked my interest in IEMs and their potential. Purchased a pair of customs and am awaiting their arrival. I also borrowed earphones from a friend (Westone 4s) to do a little bit of comparison after reading about the issues. I then tried EQing the 4.Ai around the ~4.1khz area, and after critical listening I can indeed hear a dip in that range.
Does knowing that a dip exists affect me in a very negative manner? No, not at all. The existence of the dip and my knowledge of it doesn't prevent me from enjoying the 4.Ai. I still think the IEM performs well on most genres save orchestral music, complex classical pieces and acapella.
From the manufacturing side, it would be interesting to hear a clarification on whether the dip was an intended design in the sound signature of the 4.Ai or not.