code: function(size) { 
          if (this.singleTile) {
              size = this.map.getSize();
              size.h = parseInt(size.h * this.ratio, 10);
              size.w = parseInt(size.w * this.ratio, 10);
          } 
          OpenLayers.Layer.HTTPRequest.prototype.setTileSize.apply(this, [size]);
      }
docs: APIMethod: setTileSize
  Check if we are in singleTile mode and if so, set the size as a ratio
  of the map size (as specified by the layer's 'ratio' property).
  
  Parameters:
  size - {<OpenLayers.Size>}