Custom similarities in ElasticSearch Nest 2

Elastic Stack Elasticsearch
6

Nope it's not there:

{
  "topic-201607271639": {
    "aliases": {
      "topic-read": {},
      "topic-write": {}
    },
    "mappings": { ... }
	"settings": {
      "index": {
        "creation_date": "1469633972582",
        "analysis": { ... }
		"number_of_shards": "3",
        "number_of_replicas": "0",
        "uuid": "5hp7_rVdQeGZS_h3_mibKg",
        "version": {
          "created": "2030499"
        }
      }
    },
    "warmers": {}
  }
}

Here's my create index call:

var createIndexRequest = new CreateIndexRequest(newIndexName)
                                     {
                                         Aliases = new Aliases(new Dictionary<IndexName, IAlias> {{GetWriteAlias(), new Alias()}}),
                                         Similarity = new Similarities(new Dictionary<string, ISimilarity> {{"default", new CustomSimilarity()}}),
                                         Mappings = new Mappings {...},
                                         Settings = new IndexSettings
                                                    {
                                                        NumberOfReplicas = 0,
                                                        NumberOfShards = 3,
                                                        Analysis = new AnalysisDescriptor().Analyzers(...)
                                                            .TokenFilters(...)
                                                    }
                                     };
var response = client.CreateIndex(createIndexRequest);

And here's my similarity:

public class CustomSimilarity : ISimilarity
{
    public string Type
    {
        get { return "my.similarity.MySimilarity"; }
    }
}

I wasn't sure whether that Type string should point to the similarity class or the plugin class but I have tried both and the result is the same.