The bulbs in flashlights and in headlights are also usually in front of the reflective material but also sometime surrounded by it, that's what they are there for, to make the light brighter and make the beam more directional. Without it all you have is a small halogen bulb that doesn't cast as much light.
In this case if the inside of the hood is shiny then it is reflecting the light all the way to the end of the hood and is still going to produce a HALO when it exits the end of the hood. By making it darker or painting it flat black, you cut down on the amount of reflection, thus cutting down on the amount of halo at the end of the hood. The amount of light doesn't get any more or less intense, because the light is being made at the spotlight not in the hood.
