Do they go in just as far as a tampon, or further?

To explain the question, I have had some horrible situations with tampons and menstral sponges, requiring trips to hospital. A later ultrasound of my internal bits showed that I have an "extra long" uterus and vagina, according to the Dr. This is a pain in the bum becuase it also means I need extra long toys to feel nice :-P but I also can't use tampons anymore becuase, as I discovered, I either can't get them up far enough and they fall out, or I magically manage to shove them up far enough and they get stuck and disapear, requring a hospital visit to remove them. The string doesn't even reach out. This limits me to horrible, horrible pads.

So...can you sleep in the cup? How does that work? It doesn't tip out becuase of the changing angles of the body during sleep?

I have heard of them before but becuase I never had a person to ask questions to about them, never thought to try one. I am intrigued.