Analyzed string fields take term positions into account, in order to be able to support proximity or phrase queries. When indexing an array of strings, each string of the array is indexed directly after the previous one, almost as though all the strings in the array had been concatenated into one big string.
This can result in matches from phrase queries spanning two array elements. For instance:
position_increment_gap can introduce a fake gap between each array element. For instance:
The first term in the next array element will be 50 terms apart from the last term in the previous array element.
The phrase query no longer matches our document.
position_increment_gap setting is allowed to have different settings
for fields of the same name in the same index. Its value can be updated on
existing fields using the PUT mapping API.