The diameter of the pie relative to the plot area. Can be a
percentage or pixel value. Pixel values are given as integers. The
default behaviour (as of 3.0) is to scale to the plot area and give
room for data labels within the plot area.
slicedOffset is also included in the
default size calculation. As a consequence, the size of the pie may
vary when points are updated and data labels more around. In that
case it is best to set a fixed value, for example "75%".