The value is the maximum angle between the normals of two adjacent faces, beyond which they won't be smoothed.
So if the normals are 50 or more degrees apart, no smoothing will be performed across the corresponding faces.
Try lowering the number. If it doesn't work, try using the global HLRAD parameter
-smooth # instead, where # is the value. It'll affect all faces, but at least we'll be able to find out if it works at all.