Atlas=vented as dynamic, and Comet = sealed ba, so neither should in theory have flex.
Still tempted to get an e5000 or 4000,
From the review, Atlas seem to have only back volume vent, so that's probably why it's flex like crazy since the air in front of the driver have nowhere to go.
Also I don't think dynamic driver iem need vent though as my old ath e40 don't have any vent hole.