I think one issue is the containment factor. The pot 'helps' keep the lilly in check. See the current post below.

Here is a link that might be useful: big lilly

They will live like this but to thrive and bloom their best they need clay garden soil and a lot of fertilizer.

Hi
Don't know if there's a big difference between tropical and hardy types. But over the years I've experimented with all kinds of methods with the tropical lily Blue Goddess. In a 15" cubed pot with oil dri clay fed with fruit tree spikes it produced 14 inch flowers standing two feet out of the water.. In regular soil in down to 12 inch pots it produced a max of 5 inch flowers never more than a foot out of the water. have even grown offsets in a 150 gallon aquarium , removing all floating pads . grew with submerged ruffled leaves that looked much like lettuce having a red cast .Never any flowers .had to remove it from the tank as it covered two thirds of the tank. Might mention "removing all but one or two buds which flowerd at 17 inches wide but still a max of 24 inches above the water, Only "method" that resulted in death of the plant was a complete drying out . Incredibly adaptable plant for sure lol gary