I think you are correct. I had a very large catnip on the SE side of the house, under the overhang so no rain reached it most of the time. It was very happy there. Then last year, the rain gutter clogged (dead something in the gutter) but we didn't realize it for about a month, during which time the gutter overflowed where the catnip was whenever it rained.... The catnip drowned.
Happily, it had somehow started a daughter patch a little way off at the edge of a garden bed. That one is in morning shade but VERY dry spot due to the oak tree on the other side of the fence reaching in with its roots and sucking up everything it can. It's doing fine and expanding.