Status Panel with OpenTSDB

I have a Status Panel using an OpenTSDB Data Source.
For the Alias, I’m trying to use $tag_instance, but when that is used, the Status Panel will not show any data. If I use just text in the Alias, then it will (but then I have the same alias for all instances).
In this particular case, I’m trying to use Disk Free Space as the metric, which I have multiple drives to show, which is the “instance”.