Insufficent Metrics Data for Live Apps

We are trying to query our perf and metrics data through the ASC API, and are finding that it returns empty JSONs.

Looking in xCode's Organizer we see the same result, with the addition of an 'Insufficient Metrics Data' label.

The apps in question are live with a couple thousand users, I was wondering if we could get any information on what scale needs to be reached in order to extract this metrics data?