Facebook API insights/page_storytellers_by_city returns no results but by_story_type does

I'm using the Graph API Explorer of Facebook to request page storytellers, but for some reason I only get results when I request them by story type (so: page_storytellers_by_story_type). When I try the documented page_storytellers_by_city or page_storytellers_by_country the result I get is empty.

<batch_id>/insights/page_storytellers_by_story_type result:

"values": [
        {
          "value": {
            "fan": 2, 
            "page post": 1
          }, 
          "end_time": "2015-02-21T08:00:00+0000"
        }, 
        {
          "value": {
            "fan": 2, 
            "page post": 1
          }, 
          "end_time": "2015-02-22T08:00:00+0000"
        }, 
        {
          "value": {
            "fan": 2, 
            "page post": 1
          }, 
          "end_time": "2015-02-23T08:00:00+0000"
        }
      ]

<batch_id>/insights/page_storytellers_by_country result:

"values": [
        {
          "value": [
          ], 
          "end_time": "2015-02-21T08:00:00+0000"
        }, 
        {
          "value": [
          ], 
          "end_time": "2015-02-22T08:00:00+0000"
        }, 
        {
          "value": [
          ], 
          "end_time": "2015-02-23T08:00:00+0000"
        }
      ]

What I might be doing wrong?