Interesting charts. I have owned HFI650 for a short time, enough to equalize it.
The dips (different from my pair) are actually ringing, but not all that long. 12.5k peak was quite annoying without eq, giving sound a really brittle feel.
That headphone is probably the least ringing of the Ultrasone offerings, but channel matching in the high end was off, giving soundstaing a really weird feel.
Very sensitive to head placement and the optimal one caused them to slip off the head at times.
In case you're interested, I still have the old correction curve.
Not my usual standard of precision, but it should give you an idea exactly how flawed my pair was.
At least they're consistently sucking, I give them that.