Hi Martin,
By default, Elasticsearch will return the buckets for the top ten terms ordered by the doc_count.
We use the default behavior because the higher the requested size is, the more accurate the results will be, but also, the more expensive it will be to compute the final results.
To solve your problem we could extend our query and provide size of term buckets that should be returned out of the overall terms list. It will be a new feature.
Best regards
Irina