When the RowTotalsLocation property is set to FieldRowTotalsLocation.Tree, calling the BestFit method for row fields has no effect. In this instance, to apply best fit to row fields, use another overload of this method, which takes the area parameter, and pass the FieldArea.RowArea value as this parameter.
Note
The Best Fit is available only after the Pivot Grid Control has been loaded in the visual tree.
To learn more, see Best Fit.