OfficeChartPictureType
Specifies how pictures are displayed on a column, bar picture chart, or legend key.
stack = 0
Indicates picture is sized to repeat a maximum of 15 times in the longest stacked bar.
stackScale = 1
Indicates picture is sized to a specified number of units and repeated the length of the bar.
stretch = 2
Indicates picture is stretched the full length of stacked bar.