By default the 2D physics visualization is drawn at DrawBasics2D.Default_zPos_forDrawing. You can use a custom z position only for the 2D physics visualization. Setting this "custom_zPos_forCastVisualisation" to "float.PositiveInfinity" means: Ignore "custom_zPos_forCastVisualisation" and use DrawBasics2D.Default_zPos_forDrawing.