Hi Mary Ellen,
I have full open pans, and I fill with about 2 inches of pine.
Some cages the pan fits into the cage, and others the cages fit into the pan.
It's easier to drop the cage down into a pan, though that means the bottoms will get soiled faster,ei they'll pee on post corners and wood will soak up the pee.
If you put a pan into a cage that does not have a slide out bottom, you'll need extra room to get it in. The pan will not fit tight.
Placing a strip on 2 edges will be required to fill the little gaps.
These will also jam the pan in place.
So I don't really have to train, some do get lazy though.
Have you seen one let his behind hang over a ledge and pee.