i tested this Acoustune AET16 tips for my ER4XR because i saw that the output nozzle diameter is small, similar to the original triple flange, and i'm happy to report that it doesn't muck up the treble response and sounds similar to the triple flange.
my usual dual flange eartips that i got from cheap Yotaphone IEMs also sounds similar to the original triple flange, but i have to make smaller bore adapter to make them fit the Ety's small nozzle, and also the AET16 is much more stable in keeping seal when moving (the Yota's tips sometimes break seal).
other tips that I've tried (like the shure's and westone's) fit fine, but all of them changed the sound too much for my liking.
overall I'm quite happy with this finding. i will buy some more for my ER4PT (and maybe try a smaller size to see how it goes)