Searchpanes not working with AJAX data

I first setup SearchPanes with data from the DOM and it worked just fine.

However when I load the same data in via an AJAX source the custom function for SearchPanes nolonger return results.
The filter labels appear, but without any results?

    {searchPanes: {
                     options: [
                                             {
                             label: 'Under 20%',
                             value: function(rowData, rowIdx) {
                                 return rowData[2] < 20;
                             }
                         }
                       ]
                   },
  targets: [2]
                 },

Is there a problem with my function or do I need to look elsewhere?
(non-custom searchpanes do appear)