A user wants to customize the InnerPlotPosition and CustomPosition properties of chart area in our ReportDesigner and ReportViewer as like in the MS report builder.
CustomInnerPlotPosition - This property is to customize the position of the chart inner plots i.e Plotted Visuals such as line, bar, column, etc.
CustomPosition - This property is to customize the position of the Chart area. i.e inner plot area and axis labels.
Reference link: http://www.douglane.net/fit-chart-labels-in-ssrs/