Answer: Lobelia demand good drainage. If kept too wet, root or crown disease problems will quickly destroy a plant, especially in the heat of summer. I doubt your plants will come back if a root or crown disease destroyed them.
We often see a plant survive a condition that kills its neighbors. The reason why is difficult to say, but in this case may be due to the smaller pot. It is easier to overwater a plant that is small for the container size. There is more soil that the roots can fully colonize and the soil tends to stay wet longer.
Make sure your containers have drainage holes and ease up on the water...moist but not soggy.
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