This is a known issue already logged in our system for improvement.
Until there is a fix, you can analyze the data at run-time and set the axis's Scale.Maximum to a value allowing the curve to be drawn without clipping.
//at run time
//Assuming you have a single Cartesian coordinate system in your graph.
var cartesianCoordinateSystem = (Telerik.Reporting.CartesianCoordinateSystem)graph.CoordinateSystems;
//Assuming your Y axis has a numerical scale.
var numericalScale = (Telerik.Reporting.NumericalScale)cartesianCoordinateSystem.YAxis.Scale;
numericalScale.Minimum = 1;
numericalScale.Maximum = GetMaximum()+1000;
I hope the above information is helpful.
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