Is it possible to solve the following problem with a SINGLE QUERY?

Basically I’m looking for a solution to solve the following problem. Since there’re hundreds of such operations at each moment, the operation needs to be FAST.

So I have a curves collection with documents like this:

{
    curveId: 12,
    values: [1, 2, 12, 7, ...]
}

Suppose I’d like to set a curve value at index 3 and result in:

{
    curveId: 12,
    values: [1, 2, 12, new_value, ...]
}

in case of no matched curveId, a new curve is created:

{
    curveId: 12,
    values: [null, null, null, new_value]
}

so I write this upsert query:

db.curves.update({
    curveId: 12
},{
    $set: { "values.3": new_value }
},{
    upsert: true
})

This works when there’s a matched document. However, if there’s no match, it will create a new element like this:

{
    curveId: 12,
    values: { '3': new_value }
}

Not what I was expecting.

I’ve googled quite some time but found no solution yet. Is it even possible to solve the problem with one query?

Thank you.