Query string with boost fields in Elastic Search

I am using Query String with Boost Fields in Elastic Search 1.7. It is working fine but in some scenario, I am not getting expected result.
Query:

query
{
   "from": 0,
   "size": 10,
   "explain": true,
   "query": {
      "function_score": {
         "query": {
            "query_string": {
               "query": "account and data",
               "fields": [
                  "title^5"
                  "authors^4",
                  "year^5",
                  "topic^6"
               ],
               "default_operator": "and",
               "analyze_wildcard": true
            }
         },
         "score_mode": "sum",
         "boost_mode": "sum",
         "max_boost": 100
      }
   }
}

Sample Data :

{
   "took": 50,
   "timed_out": false,
   "_shards": {
      "total": 5,
      "successful": 5,
      "failed": 0
   },
   "hits": {
      "total": 4,
      "max_score": 12.833213,
      "hits": [
         {
            "_id": "19850",
            "_score": 12.833213,
            "_source": {
               "ID": "19850",
               "Year": "2010",
               "Title": "account and data :..."
            }
         },
         {
            "_id": "16896",
            "_score": 11.867042,
            "_source": {
               "ID": "16896",
               "Year": "2014",
               "Title": "effectivness of data..."
            }
         },
         {
            "_id": "59862",
            "_score": 9.706333,
            "_source": {
               "ID": "59862",
               "Year": "2007",
               "Title": "best system to..."
            }
         },
         {
            "_id": "18501",
            "_score": 9.685843,
            "_source": {
               "ID": "18501",
               "Year": "2010",
               "Title": "management of..."
            }
         }
      ]
}

I am getting above sample data by using query and that is as per expectation. But now, If I increase weight of year to 100 then I expect 4th result at 3rd position and 3rd result at 4th position. I tried many things but I don't know what I am doing wrong.