resize bar in bar graph to be universal size

[louisawang]

I have a bar graph with 3 fields labelled Memory, CPU and Disk Space. When there is no Memory value, only CPU and Disk space will show. However, the size of the bar will become fatter as less fields are being shown. Take for example:
It only shows disk space and CPU

vs

where there is only one field and the size of the bar is bigger. How do i make it so its the same size no matter how many fields?
This is the code for the graph:

        <option name="charting.chart">bar</option>
        <option name="charting.chart.barSpacing">10</option>
        <option name="charting.chart.stackMode">stacked</option>
        <option name="charting.drilldown">none</option>
        <option name="charting.fieldColors">{"Green":#8BC647 , "Available":#A9A9A9, "Amber":#FCB54E, "Red":#EE2E55}</option>
        <option name="charting.legend.placement">bottom</option>
        <option name="height">350</option>
        <option name="refresh.display">progressbar</option>