I'm not sure it ever stops... I do know when going back to other IEMs from the HJE900 is more of a shock than I'm used to with other IEMs. Even when playing around with EQ and giving the two IEMs a frequency response that's equal, the HJE900s maintain their unique sound.
Given their unique signature, I think these more than other IEMs have a presentation that takes some getting used to, until the idiosyncratic presentation becomes familiar enough to be transparent.
For me the mids seem right now, not recessed. I notice that in mp3s from vinyl rips of old music the phones sound balanced to me... But in modern masterings the bass can be too heavy and treble harsher.... I think it's artifacts of dynamic range compression in modern recordings.