Elastic search group two fields to single field without copy_to parameter

Question

The problem

I have object employee with two separate properties:

• FirstName
• LastName

For relevant ordering I must use match_phrase parameter, cause match_phrase provides better relevance depending on word order.

I tried use copy_to parameter for copy first and last names to eng_full_name field, but unfortunately as I understand copy_to doesn't provide tokens ordering, that important in phrasal matching.

And request below not working

    GET agreements/_search
    {
      "query": {
        "match_phrase": {
          "eng_full_name": {
            "query": "Kimberly Smith",
            "slop": 4, 
            "boost": 25
          }
        }
      }
    }

I can't don't use match_phrase because slop parameter required in the context of the task.

Is it possible to configure copy_to order. If no does i have some alternative way?