I have exactly the same question, I spend a couple of hours on this since I noticed that with {:array, :map} the data is not stored as JSON but as a JSON string!
Seems that there is something mixed up. What I do know is that {:array, :map} is the adapter generic way of saying you want to store embedded records independent of the database you are using. For Postgres this should map to JSONB but apparently it does not or does in a strange way.
