As you can see on the screenshot, the diamond turns into a triangle.  Here is the code

    current.MarkerStyle.Visible = true;
     current.MarkerStyle.PointShape = PointShape.Diamond;
     current.MarkerStyle.Width = new NLength(20);
     current.MarkerStyle.Height = new NLength(10);
     current.MarkerStyle.Depth = new NLength(0);
     current.MarkerStyle.VertAlign = 0;

If i changed Height to 20 then it becomes a diamond that looks like a square rotated 45 degrees.