In my environment I used the HiddenChartFormatter parameter charting.layout.margin to solve the right hand edge clipping of the chart.
<module name="HiddenChartFormatter">
<param name="charting.chart.stackMode">stacked</param>
<param name="charting.legend.placement">bottom</param>
<param name="charting.chart">bar</param>
<param name="charting.layout.margin">(0,125,10,0)</param>
.
.
.
Where the numeric values set the left, right, top, and botom margin of the chart in the panel.
http://docs.splunk.com/Documentation/Splunk/latest/Developer/AdvChartingConfig-LayoutData
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