I don't actually see any substantive difference between the two charts in Excel 2007. I think that you probably want to avoid writing a data series on the chart for the first row of each data array:

    ...
    if ($i > 1) {
        $chart->add_series(
            'categories' => xl_range_formula( 'testRight', 1, 1, 1, 13
+),
            'values'     => xl_range_formula( 'testRight', $i, $i, 1, 
+13 ),
            'name'       => $_->[0],
        );
    }
    ...

[download]

In which case the issue is more evident.

Unfortunately, what you are seeing is a results of Excel's automatic axis scaling. There isn't (and probably won't be) any way to override this with Spreadsheet::WriteExcel. It is intended as a feature in Excel::Writer::XLSX but even that is probably a few months off.

Update: Manual scaling is now supported in Excel::Writer::XLSX >= version 0.36.

--
John.