system
A chat on subreddit /r/me_irl
human
The bigger you are, the more of it stays out. While quite flexible, vaginas can't stretch out indefinitely. I think all it takes is 7-8 inches to hit the cervix so if a guy is lucky enough to be bigger than that, he'll probably never be balls-deep in it. 

Now of course, some girls may love getting their cervix bruised, but truth be told, girth is usually more important that length (obviously having both is ideal lol). Adding to that the fact that many women (especially younger ones) have no idea how much is 6 inches, you can be pretty sure that yes, porn has lied to us all lol.
gpt
Little peepee here, have hit many cervixes and it’s not sexy.

You just spend a lot of time awkwardly apologizing with a sad boner while your associate in coitus curls up on the bed with cramps for half an hour.

“Can I get you anything? Snacks? Alcohol?…”