I should note that I previously used the Diva Cup until I lost it (yeah, I don't know how I lost it but I did!) and I don't remember it sitting as high as the Lunette did. I'm pretty sure the Lunette is longer than the Diva though, just going off of how I remember them looking, so that makes no sense.
So is the process of pulling it down by the stem creating a suction? Is that what could suck the IUD out?