Keep in mind that the new Nova Extreme Pro has been re-worked and does have individual reflectors. The older models used the Parabolic reflector and SUCKED!! Typically, the dawn to dusk ballast turns on the two outer bulbs. That would depend on the fixture brand though. Sunlight Supply Tek5 fixtures turn on the 2 outer bulbs. Hmmm, just thought of something... that's how they work on the 6 bulb fixtures. With an 8 bulb fixture, I don't know.
As to the reflectors, the newer models don't actually have individual reflectors. What they are is a reflector that's molded around each bulb, in a "gull wing" pattern. This creates much better reflection than their old parabolic reflectors. Very similar to the Tek5 units.