Incorrect (nonexistent) tiles at zoom level 11

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Using this geoJson at zoom level 11
```
{
"type": "FeatureCollection",
"features": [
{
"type": "Feature",
"properties": {},
"geometry": {
"coordinates": [
[-107.57474911721675, 37.765903789097095],
[-107.57384175953081, 37.75616186145916],
[-107.50425513238076, 37.71049221239559],
[-107.4731808734297, 37.62036834873592],
[-107.47599073203504, 37.61112403824043],
[-107.47295160433036, 37.599860534562524],
[-107.45664930903803, 37.59101553690758],
[-107.44956219593156, 37.56375515522157],
[-107.4410913786216, 37.55329488693623],
[-107.44463546019313, 37.54102064839029],
[-107.44368651302858, 37.50716987497118],
[-107.43132230490518, 37.497378059487716]
],
"type": "LineString"
}
}
]
}
```

I should be getting something around [412, 792, 11] according to [what the tile](https://labs.mapbox.com/what-the-tile/). Instead I'm getting `[ [ 240, 1286, 11 ], [ 240, 1386, 11 ], [ 240, 1486, 11 ] ]`.

Reproduce the GeoJSON example at zoom level 11 and compare tile-cover's returned coordinates with the expected tile from the linked What the Tile reference. Trace the tile-generation entry point to determine why the returned tiles differ, then add or update coverage for this geometry and verify the output matches the expected tiles.

Written by the indexing model from the issue text.