Shards skip on range query

[jimyoo]

Based on this thread, I am testing range queries to see skipping shards but the result is not I expected.

I have 2 indices (5 shards each with 0 replica); "event-1" and "event-2" where "event-1" has 4 documents whose "created (date type)" are from 1536943171000 to 1536946771000 and "event-2" has from 1536946772000 to 1536946780000.
With a query like under, I expected see "skipped" 5 shards but 0 and all 4 hits from event-1.

POST event-*/_search
{       
  "size": 10, 
  "query": {
    "range": {
      "created": {
        "gte": 1536943171000, 
        "lte": 1536946771000  
      } 
    }   
  }     
} 

{
  "took": 2,
  "timed_out": false,
  "_shards": {
    "total": 10,
    "successful": 10,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": 4,
    "max_score": 1,
    "hits": [
      {
        "_index": "event-1",

Can you please let me know what I need to check or understand?
I have tested with Elasticsearch version 5.6 and 6.2 and results are same.