Use query match only to boost and don't increase the recall set

I have multiple match queries inside the should clause. I would like to add another field match, which should be used only to boost scores and not increase the recall set.
I have the below query that is being used currently:

{
  "query": {
    "function_score": {
      "query": {
        "bool": {
          "minimum_should_match": 1,
          "should": [
            {
              "multi_match": {
                "minimum_should_match": "2<50%",
                "query": "cadbury sugar free chocolate",
                "type": "best_fields",
                "fields": [
                  "name^10",
                  "description^5"
                ],
                "tie_breaker": 1
              }
            },
            {
              "term": {
                "name.raw": {
                  "value": "cadbury sugar free chocolate",
                  "boost": 10
                }
              }
            },
            {
              "nested": {some nested should query}
            },
            {
              "nested": {some nested should query 2}
            }
          ]
        }
      },
      "functions": [
        {some function boost},
        {some function boost 2}
      ],
      "score_mode": "sum",
      "boost_mode": "sum"
    }
  },
  "from": 0,
  "size": 20
}

As you can see I have 4 matches in should among them, either one match is mandatory for a document to be relevant.

Now I need to introduce a new field brand. From the above result set all the documents should be boosted that have brand:cadbury but should not extract any new document that matches this condition.
I tried adding one more match(with boost) inside should for the brand field, but this increases my recall set.

How do I solve this?