[MapProxy] Overriding cache-only WMTS GetCapabilities reponse.

[Smart, Gary Export License Required - US Collins]

I am using MapProxy to serve an MBTiles file (treated as a cache only source) as a WMTS.  The getCapabilities response from such a WMTS has a BBox -180/-85 to 180/85.  However, I know that the tiles in the set are much more localised and wish to impose a BBox ans min/max scale on the layer.  Unfortunately there appears to be no way to apply a BBox to a cache (only to a source - which this scenario doesn't have because the whole tile set is served from the MBTiles file as if it were a cache).
Is it possible to impose a BBox on a cache, and if not, is it possible to otherwise correct the GetCapabilities response?

The Cache part of the YAML is:

caches:
  my_mbtiles_file:
      sources: []
      grids: [GLOBAL_MERCATOR]
      cache:
                type: mbtiles
                filename:  /location/of/my/file.mbtiles

There are no sources in the YAML.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/mapproxy/attachments/20190312/70363f1d/attachment.html>