7.x How do remove duplicates in search after query?

I have several indexes spread across 3 shards that hold my data. I want to make a SearchAfter where I fetch 50 rows ordered by start time. When I run it I am returned 50 hits but half of them are duplicates as the data is spread to several indices. I thought it was to the query then detach approach but even after I switch to DfsQueryThenFetch I still return duplicates. How do I filter out duplicates (preferably by guid field)? Code below

    //reduced for brevity
        List<resultObjects> result = new List<resultObjects>();

        DateRangeQuery dq= new DateRangeQuery()
        {
            Name = "StartTime",
            Field = "StartTime",
            GreaterThanOrEqualTo = from,
            LessThanOrEqualTo = to
        };

        TermQuery tq1= new TermQuery()
        {
            Name = "Location",
            Field = "Location"
            Value = "sds"
        };

        BoolQuery boolQuery = new BoolQuery();
        boolQuery.Filter = new List<QueryContainer>() { dq, tq };
        boolQuery.Must = new List<QueryContainer>()
        {
           new MatchQuery() 
                {
                Name = "user",
                Field ="user",
                Query= "test"
                }
        };

        var searchRequest = new SearchRequest("data_index_*");
        searchRequest.SearchType = SearchType.DfsQueryThenFetch;
        searchRequest.From = 0;
        searchRequest.Size = 50;
        searchRequest.Query = boolQuery;
        searchRequest.Sort = new List<ISort>
        {
            new FieldSort { Field=Infer.Field<resultObjects> 
              (p=>p.StartTime),Order=SortOrder.Ascending}
        };

        if (searchAfterTime < to)
            searchRequest.SearchAfter = new List<object> { searchAfterTime };

Which of the duplicates should Elasticsearch use though, the one with the newest StartTime? If so then consider also adding a top hits agg on that field.