In the meantime, I thought I'd describe how I use my cup, in case anyone else with a tilted cervix needs help with theirs. I asked my doctor and although I don't have a true "tilted uterus," it is off-center (on the left) and the os faces the left corner when it's relaxed.
I can't get away with inserting it low and letting it find its own way. The muscles bring it to the center where it is no help. Instead, I insert it, trace my finger to the left side to see if it's peeking, and then press up and left on the cup. Having a stemless one works well for this. I seem to have to be more aggressive than most people to make sure it's actually around my cervix. When it's not, the blood seems to just drip down the left wall past the cup.
I now have to change it every 6 to 8 hours, not because it's full, but because the muscles attempt to bring the cup into the center, and away from my cervix after a while. I find I can feel it leaking long before anything will actually come out of my vagina. It's easy for me to sense when this is happening.
Now for a question: I have about 4 open boxes of tampons in my bathroom being useless. Are there any charities that will take open boxes? They're all individually wrapped but all the charities I've looked up say they will take unopened boxes. I'm not exactly "tampon sharing" close with too many menstruating women and I don't want them to go to waste.