Add multiple Elasticsearch metrics for variable in single panel

Grafana Elasticsearch
1

I have a template variable setup $avgs which gives me [a1.avg, a2.avg, a3.avg]
My Elasticsearch records are structured like

{
    "a1": {
        "avg": 12
    },
    "a2": {
        "avg": 24
    },
    "a3": {
        "avg": 36
    }
}

I need a query which shows sum of a1.avg, a2.avg, a3.avg when all option is selected.

If I select only a1.avg from dropdown, I am able to see graph, but cannot see multiple lines plotted if I have multiple/all selected.

when I select a1.avg from dropdown

a1.avg
a1.avg2520×1176 183 KB

when I select all from dropdown

all
all2520×1282 215 KB

I am pretty sure that my query is wrong, but did not find any resources on how to structure this query to show multiple metrics for multi valued variable.

PS: I already tried having multiple panels when multiple values are selected. But I want all of them in single panel.