Shifts in placement and leakage

Okay, here's the skinny:
I am 21.
I have a Keeper Moon Cup B.
I have had it and used it for every period since May.
During the earlier, heavier part of my period (heavier bleeding is typically confined to the first day or two, and is not extremely heavy) it sometimes leaks badly, especially on waking up in the morning. Even towards the end I sometimes find small traces of blood around it while it is still inserted, though not enough to have leaked out and caused spotting.

I assure you, I UNDERSTAND the principal of how to insert it and get a good seal. it is comfortable, easy to insert and remove, and I do not notice it during wear. What I think is happening is that during long periods of wear when I am relaxed (like while sleeping through the night), it actually travels upwards out of its correct position. When I go to remove it, it seems much higher and I have to sort of "dig around" and pull it out a considerable ways.

Does this mean that this size and brand of cup is a, too short and I need a longer one, b, too narrow and I need a larger one, or both, or something else? Please advise.

I actually think you are correct on both points. You sound like you're inserting correctly and all. So if most of the leaking is on heavy days, then its probably because you need more capacity. True, emptying it more often really helps to prevent it, but if your flow is kind of heavy on some days, having to empty too often can be a pain. I like to empty the cup right before I go to bed, but for some people, they still need mreo capacity because that doesn't even help.

Also, if its hard to reach, a longer cup can help. Not sure if the blood you see on light days leaking, it might be "residual slobber", just the little bit of blood leftover on the outside of the cup after insertion.

Does it leak the entire time on heavy days, or after a certain amount of time? If its only after a certain amount of time, then it is a capacity issue. But if its all the time, like even right after you insert-- then your body probably just doesn't like the shape of that particular cup.

In case its a capacity thing, cups that are a little longer in the body than a Keeper, and hold more liquid are:

Divacup (medium stiffness)
Miacup (flat stem, very squishy)
Large Lunette (flat stem, firm)
Mpower (flat stem, firm)
Large Fleurcup (flat stem, firm)
Large Yuuki (more squishy, but its really big)
Large Meluna (medium stiffness, different stem choices)

Hope this helps