How do you draw poses like this?

Do artists reference real porn for this or something? Some of these shots seem like stuff you wouldn't find them in porn like the bird's eye view on the bottom here.

People have said to just put the figures in boxes and rotate them. I tried that but I don't know where the box ends or begin in perspective for figures or how big or smaller the box gets.
I tried it but i feel like maybe i might have made the box get way too small further away or I might be wrong and it's right and the box is meant to get this much smaller, however i have no clue which is right.
I also extended a line from the end of her torso but even then I feel like it's wrong.
How am I supposed to put figures in boxes and know how much bigger, smaller boxes are.