^It might be the air and tactility that the treble creates, and not the mids, as the HE-400 (treble aside) has dark (and therefore possibly thicker) mids. Or perhaps you like your bass dry and not full sounding? Or is the lower mids the problem for you when it becomes too thick and overwhelming?
Might be that I like Dry Bass, althoiugh the biggest issue though is the lack of Upper Mids, those are wwhat have a nice edge to them. ALL Low mids= mush without any upper tactility. Treble has a distinctly different feel to it