ElasticSearch 2 bucket level sorting

Elastic Stack Elasticsearch
1

Hello,

I am stuck on this from last two days. The mapping of database is this:

    {
   "users": {
      "mappings": {
         "user": {
            "properties": {
              credentials": {
                  "type": "nested",
                  "properties": {
                     "achievement_id": {
                        "type": "string"
                     },
                     "percentage_completion": {
                        "type": "integer"
                     }
                  }
               },
               "current_location": {
                  "type": "geo_point"
               },
             "locations": {
               "type": "geo_point"
         }
            }
         }
      }
   }

Now In the mapping, You can see there are two geo-distance fields one is current_location and other is locations. Now I want to sort user based on credentials.percentage_completion which is a nested field. This work fine for example this query,
Example Query:

GET /users/user/_search?size=23
{
  "sort": [
    {
      "credentials.percentage_completion": {
        "order": "desc",
        "missing": "_last"
      }
    },
 "_score"
  ],
  "query": {
    "filtered": {
      "query": {
        "match_all": {}
      },
      "filter": {
        "geo_distance": {
          "distance": "100000000km",
          "user.locations": {
            "lat": 19.77,
            "lon": 73
          }
        }
      }
    }
  }
}

I want to change sorting order made into buckets, the desired order is first show all the people who are at 100KM radius of user.current_location and sort them according to credentials.percentage_completion and then rest of users sorted again by credentials.percentage_completion.

I tried putting conditional in sorting and made it multilevel but that will not work because only nested can have filters and that on nested fields child only.

I thought I can use _score for sorting and give more relevance to people who are under 1000 km but geo-distance is a filter, I don't seem to find any way to give relevance in filter.

Is there anything I am missing here , any help would be great.

Thanks