public double ScaleFactor {get; set;}

{
  // Note: call within QueuedTask.Run()
  {
    var def = pointCloudSceneLayer.GetDefinition() as CIMPointCloudLayer;

    //Set the point shape and sizing on the renderer
    def.Renderer.PointShape = PointCloudShapeType.DiskFlat;//default
    var scaleSize = new CIMPointCloudSplatAlgorithm()
    {
      MinSize = 8,
      ScaleFactor = 1.0 //100%
    };
    def.Renderer.PointSizeAlgorithm = scaleSize;
    //Commit changes back to the CIM
    pointCloudSceneLayer.SetDefinition(def);
  }
}