Help with `docCount`

[tiagokalinke (TIAGO KALINKE IORI)]

Hi. I am using the Explain API to understand the relevance of a result. However, for each request the docCount is varying.

    {
        "size": 6,
        "query": {
            "bool": {
                "must": [
                    {
                        "function_score": {
                            "query": {
                                "bool": {
                                    "should": [
                                        {
                                            "multi_match": {
                                                "type": "most_fields",
                                                "query": "roma",
                                                "fields": [
                                                    "canonicalName",
                                                    "keywords",
                                                    "name",
                                                    "code"
                                                ],
                                                "boost": 1,
                                                "operator": "and"
                                            }
                                        },
                                        {
                                            "multi_match": {
                                                "type": "phrase",
                                                "query": "roma",
                                                "fields": [
                                                    "name",
                                                    "canonicalName"
                                                ],
                                                "boost": 1,
                                                "operator": "and"
                                            }
                                        },
                                        {
                                            "multi_match": {
                                                "type": "phrase_prefix",
                                                "query": "roma",
                                                "max_expansions": 100,
                                                "fields": [
                                                    "keywords",
                                                    "name",
                                                    "canonicalName"
                                                ],
                                                "boost": 1,
                                                "operator": "and"
                                            }
                                        }
                                    ]
                                }
                            }
                        }
                    }
                ],
                "must_not": [],
                "filter": []
            }
        }
    }

How does the calculation of this field work?

I'm using only one shard.