WMS Zoom Level blues

There are a few other issues which deal with aspects of this, but as far as I can gather, not specifically for WMS layers.

I have the following WMS layer:

$items = array();
$openlayers_layers = new stdClass;
$openlayers_layers->disabled = FALSE; /* Edit this to true to make a default openlayers_layers disabled initially */
$openlayers_layers->api_version = 1;
$openlayers_layers->name = 'icc_wms';
$openlayers_layers->title = 'ICC';
$openlayers_layers->description = 'ICC';
$openlayers_layers->data = array(
  'base_url' => 'http://shagrat.icc.es/lizardtech/iserv/ows?',
  'params' => array(
    'isBaseLayer' => 'true',
    'buffer' => '2',
    'ratio' => '1.5',
    'singleTile' => 0,
  ),
  'options' => array(
    'srs' => 'EPSG:4326',
    'TRANSPARENT' => 0,
    'exceptions' => 'application/vnd.ogc.se_xml',
    'format' => 'image/png',
    'layers' => 'mtc5m',
    'styles' => '',
  ),
  'layer_type' => 'openlayers_layer_type_wms',
);
$items["icc_wms"] = $openlayers_layers;
return $items;

Problem is the zoom levels don't allow me to get to the maximum zoom level, which I can see exists for this server via other implementations.

I have tried settings numZoomLevels as an option and even initializing a zoom level range array with no luck. The zoom bar always has the same number of elements and the maximum value is always 2 zoom levels short of the most detailed.

I would appreciate any pointers as to how to initially set the correct zoom levels for such a WMS layer, and I wonder can I achieve this adding/modifying values of the option array passed to OpenLayers.Layer.WMS() ?

Many thanks.