Hi Diganta,
Currently that is correct, afaik wildcard array index positions are not supported as yet, you have to specify fixed positions.
However substantial work is being done on enhancing array support in the product, so this is something that will hopefully show up in the future.
In the meantime you could try lifting the array object out, converting it to an array, and then performing an unnest() on it ... also coming soon I believe is a fucntion (json_array_value()?) function that will lift an array out of a JSON object directly into an array datatype.