FunctionScoreQueryBuilder should support filter mode

Elastic Stack Elasticsearch
1

Hi all, i just found a interesting issue.

enter link description here

i'm doing the elastic optimization stuffs
When run below code, average tooks 200~300 milliseconds

    {
      "from" : 0,
      "size" : 10,
      "query":
    {
      "function_score" : {
          "query" : {
                "bool" : {
                  "must" : [ {
                    "range" : {
                      "timestamp" : {
                        "from" : "1457403235000",
                        "to" : "1458008035000",
                        "include_lower" : true,
                        "include_upper" : true
                      }
                    }
                  }, {
                    "term" : {
                      "type" : "image"
                    }
                  }, {
                    "geo_bbox" : {
                      "geo" : {
                        "top_left" : [ -110.80651, 43.44131 ],
                        "bottom_right" : [ -110.804, 43.4403 ]
                      },
                    "type": "indexed"
                    }
                  } ]
                }
              },
          "functions" : [ {
            "script_score" : {
              "script" : {
                "file" : "hot_score",
                "params" : {
                  "nowTime" : "1458008709945",
                  "gravity" : "2.0"
                }
              }
            }
          } ]
        }
      }     
    }

BUT ONCE change query to filter after function_score,it's only tooks 37~38 milliseconds

    {
      "from" : 0,
      "size" : 10,
      "query":
    {
      "function_score" : {
          "filter" : {
                "bool" : {
                  "must" : [ {
                    "range" : {
                      "timestamp" : {
                        "from" : "1457403235000",
                        "to" : "1458008035000",
                        "include_lower" : true,
                        "include_upper" : true
                      }
                    }
                  }, {
                    "term" : {
                      "type" : "image"
                    }
                  }, {
                    "geo_bbox" : {
                      "geo" : {
                        "top_left" : [ -110.80651, 43.44131 ],
                        "bottom_right" : [ -110.804, 43.4403 ]
                      },
                    "type": "indexed"
                    }
                  } ]
                }
              },
          "functions" : [ {
            "script_score" : {
              "script" : {
                "file" : "hot_score",
                "params" : {
                  "nowTime" : "1458008709945",
                  "gravity" : "2.0"
                }
              }
            }
          } ]
        }
      }     
    }

So i think the filter is better than query.