Tuning Elasticsearch results

function_score inside rescore

POST /_search
{
  "_source": [ "title", "weight" ],
  "query": {
    "bool": {
      "must": {
        "multi_match": {
          "query": "Upgrade",
          "fields": [
            "title^16",
            "content_text^4",
            "display_tags^8"
          ],
          "operator": "OR",
          "type": "cross_fields"
        }
      }
    }
  },
  "rescore": {
    "window_size": 100,
    "query": {
      "rescore_query": {
        "function_score": {
          "field_value_factor": {
            "field": "weight"
          }
        }
      }
    }
  }
}