Templating group tags on nested array


I try to group by tags an array of objects.
with all the tests I did, either it selects nothing, either it selects all the objects.

the document looks to something like:
@hostname”: “argon”,
@timestamp”: “2019-04-10T10:41:50.158Z”,
“netdev”: [
@iface”: “virbr0-nic”,
@state”: “down”
@iface”: “enp3s0”,
@state”: “up”,
“recv_bytes”: 1318.0,
“recv_multicast”: 3.0,
“recv_packets”: 15.0,
“trans_bytes”: 2964.0,
“trans_packets”: 12.0
@iface”: “lo”,
@state”: “unknown”,
“recv_bytes”: 4911.0,
“recv_packets”: 21.0,
“trans_bytes”: 4911.0,
“trans_packets”: 21.0
@iface”: “virbr0”,
@state”: “down”

the group tags fileds are
tags query:
{"find": "terms", "field": "netdev.@state"}
tags value query:
{"find": "terms", "field": "netdev.@iface", "query":"netdev.@state:$tag"}

As you can see in the screenshot, this query selects all the interfaces.

Is it supported or did I made a mistake on the query line?