Can't use different size tiles for different levels

[cpmcsweeny]

I appreciate I might be doing something non standard here, but it's because of the size of my source tilesets and it ought to work. I'd like to use different sized tiles for different levels in a map, but it doesn't work - Oruxmaps uses the tilesize specified in the lowest level for all levels.

Here are my XML files:
<?xml version="1.0" encoding="utf-8"?>
<OruxTracker versionCode="2.1" xmlns="http://oruxtracker.com/app/res/calibration">
  <MapCalibration layerLevel="15" layers="false" xmlns="">
    <MapName>test2 15</MapName>
    <MapChunks datum="Ordnance Survey Great Britain 1936:MEAN FOR England; Isle of Man; Scotland; Shetland Islands; Wales@WGS 1984:Global Definition" projection="Transverse Mercator,-2,49, 0.9996012717,400000,-100000" img_height="200" img_width="200" xMax="10" yMax="10" />
    <MapDimensions width="2000" height="2000" />
    <CalibrationPoints>
      <CalibrationPoint corner="TL" lon="-2.4398420488680923" lat="52.147465297622844" />
      <CalibrationPoint corner="BL" lon="-2.4389580188255908" lat="52.05756258355327" />
      <CalibrationPoint corner="TR" lon="-2.2937026281113035" lat="52.147920042903657" />
      <CalibrationPoint corner="BR" lon="-2.2931121315091874" lat="52.058015868438261" />
    </CalibrationPoints>
    <MapBounds minLat="52.05756258355327" maxLat="52.147920042903657" minLon="-2.4398420488680923" maxLon="-2.2931121315091874" />
  </MapCalibration>
</OruxTracker>

<?xml version="1.0" encoding="utf-8"?>
<OruxTracker versionCode="2.1" xmlns="http://oruxtracker.com/app/res/calibration">
  <MapCalibration layerLevel="16" layers="false" xmlns="">
    <MapName>test2 16</MapName>
    <MapChunks datum="Ordnance Survey Great Britain 1936:MEAN FOR England; Isle of Man; Scotland; Shetland Islands; Wales@WGS 1984:Global Definition" projection="Transverse Mercator,-2,49, 0.9996012717,400000,-100000" img_height="400" img_width="400" xMax="10" yMax="10" />
    <MapDimensions width="4000" height="4000" />
    <CalibrationPoints>
      <CalibrationPoint corner="TL" lon="-2.4398420488680923" lat="52.147465297622844" />
      <CalibrationPoint corner="BL" lon="-2.4389580188255908" lat="52.05756258355327" />
      <CalibrationPoint corner="TR" lon="-2.2937026281113035" lat="52.147920042903657" />
      <CalibrationPoint corner="BR" lon="-2.2931121315091874" lat="52.058015868438261" />
    </CalibrationPoints>
    <MapBounds minLat="52.05756258355327" maxLat="52.147920042903657" minLon="-2.4398420488680923" maxLon="-2.2931121315091874" />
  </MapCalibration>
</OruxTracker>

Both layers are covering the same area, layer 15 with 10x10 of 200x200 tiles, layer 16 with 10x10 of 400x400 tiles. But when zooming to layer 16, Oruxmaps only displays a 200x200 portion of the tiles. Layer 16 works if I change the tilesize in the layer 15 XML file to 400x400 (but obviously layer 15 doesn't then work).