I suspect that this is an effect of document frequency. For instance if you have a `firstname` and `surname` field and you have a doc like this`{ "firstname" : "Paul", "surname" : "Simon"}` in the index you will very likely see it some up if you search for `simon` on both fields. The reason is that `simon` is a rare term in the `surname` field but not in the `firstname`. you can try to prevent this by changing the `type` to `type: cross_fields` see [this](
https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-multi-match-query.html#type-cross-fields) for details. If that doesn't help, I think you should provide a response from the [explain](
https://www.elastic.co/guide/en/elasticsearch/reference/6.5/search-explain.html) API
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