The only consideration I would give as far as depth is in the spring - I often move mine closer to the surface for a few weeks to get them into the warmer water and sunshine. They start growing a bit faster. Once it's consistently warm they go back to their usual spots. But in a 24 inch deep pond in zone 7 you may not even need to worry about that.
maybe.............. the plants make a lot of root mass and the tubers grow in and out of the pot. If too many grow out you have that weight pulling the edge down. But the litter and root mass is heavy so they might do ok.
Best way to know is to try. The roots might poke through the fabric of the pot.
OK That being said. I just removed a canna plant that was one and now it is three.The roots are huge. I haven't removed any Lilly's yet so will the roots become huge as will and need to be removed every year to cut the roots back?
I mainly groom tubers, in 2-3 years the roots replace all the clay, then I might remove some roots and replace with new clay.
If there is a lot of dead roots, black rotting look I will cut them out. If the lily really takes over i.e. a lot of tubers, I will then select the best, save some of the roots, and repot. I have not done a heavy grooming in about 2 years now.