These are the third IMR IEM I have owned and I experienced the same thing! Amazing OTTB. Going through a dull patch then, perking up a bit about 70 hours, then really settling into their full potential after 120 hours or so
Been going through numerous tips. Most balanced by far of the silicons is the
Final Silicon Type E - clearest of mids and clarity and -rarely- the bass is tighter with a more focused narrower band. Almost all other tips maintain a huge bass
EDIT: Just read this. Interesting . . . Might be off interest to some. Ive only tried and (very much liked) the black 'E' type. Have ordered some pink stem ones
'Final earphones can sound different depending on which eartip is used in regards of insulation and bass response. It is possible to change the bass volume and sound insulation considerably depending on the choice of eartips. Experimenting with different eartips types will result in different outcomes.
The clear version of Type E differs slightly in terms of surface fluency and hardness, and the degree to which they are airtight changes slightly. Owing to this, bass tones become a little lighter, high-pitched tones sound clear, and the sound tends toward clarity.'