Let first start you mark this thread for the old RadChart control. For new development, we urge you not to use the old RadChart but use the new RadChartView. The new chart view is actually a set of controls - RadCartesianChart, RadPieChart, RadPolarChart, ChartDataSource. It is much faster, very flexible, resolves almost all limitations the old control had and is pretty easy to set up. You can read about the differences between the components in the RadChart vs. RadChartView help article.
The connector length between that the length of the connection line between the label and the data point depends on the position of the label. This functionality cannot be modified.