Rank feature field/query on nested field

Hey guys,

I am trying to use the rank feature field/query on a nested object field.

The index is like below:
{
"id": {
"type": "integer"
},
"sources": {
"type": "nested",
"properties": {
"source": {
"type": "text"
}
},
"counter": {
"type": "rank_feature"
}
}
}

one of the example document is
{
"id": 1,
"page": "main",
"sources" : [
{
"counter" : 1,
"source" : "main"
},
{
"counter" : 10,
"source" : "browse"
}
}

Can someone please give some advise how to construct the query which can use the counter as rank feature field to boost?