Atlas Search lowerBound count behaviour

According to the documentation on counting results with Atlas Search

threshold - Number of documents to include in the exact count if type islowerBound . If omitted, defaults to 1000 , which indicates that any number up to 1000 is an exact count and any number above 1000 is a rough count of the number of documents in the result.

But when I attempt to use count with lowerBound I only get 1001 as a result, even though there are >1 million documents that match the query.

I’m having trouble finding documentation on “lowerBound” count, but my understanding of a “rough count” is an estimate, not just the threshold + 1.

Can anyone provide some insight into what’s going on here?

Here is my search stage:

$searchMeta: {
  index: 'default',
  equals: {
    path: 'workspaceId',
    value: 'foobar'
  },
  count: {
    type: 'lowerBound'
  }
}

Results: { count: { lowerBound: 1001 } }

The actual count should be 1,022,376

Thank you,
Sean