what you are explaining is Shrilly Highs that are piercing to the ears, or sibilants where the S is Sharp.
imagine a wall and a ceiling, and as the highs are produced imagine them going up the wall.
now iems with no roll off highs will go all the way up the wall to the ceiling.
now iems with roll off highs will go up the wall to a point and drop off. Roll off.
another good way to explain it is with cymbals, when a cymbal crashes with no roll off you will hear the cymbals crash and hear them all the way till they fade out. where as a cymbol crash with highs that roll off you wont hear them fade out in the high frequencies.
the shure se535 bronze and clear have roll off this isnt ideal becuase it cuts the highs short and you can miss a great ammount of detail with the highs depending on where the highs are rolling off..
now the se535-ltd-j resolve the roll off. when i got them to use my analogy the highs went straight up the way to the ceiling where i noticed that the bronze fell short, the reds surpassed them