public double SymbolScaleFactor {get; set;}

// applies to LAS dataset layers only

var lasPointsClassBreaksRendererDef = new LasPointClassBreaksRendererDefinition();
lasPointsClassBreaksRendererDef.ClassificationMethod = ClassificationMethod.NaturalBreaks;
lasPointsClassBreaksRendererDef.ModulateUsingIntensity = true;
// increase the symbol size by a factor
lasPointsClassBreaksRendererDef.SymbolScaleFactor = 1.0;

if (lasDatasetLayer.CanCreateRenderer(lasPointsClassBreaksRendererDef))
{
  CIMTinRenderer renderer = lasDatasetLayer.CreateRenderer(lasPointsClassBreaksRendererDef);
  if (lasDatasetLayer.CanSetRenderer(renderer, SurfaceRendererTarget.Points))
    lasDatasetLayer.SetRenderer(renderer, SurfaceRendererTarget.Points);
}