pff, separating the colors on Zaxxon took me much longer than expected. But no turning back now, almost done.
Rik can you make some photos of Bandai Zaxxon in action? And I'm assuming the mirror is placed right in the center of the VFD, between the big explosion and the lives-indicators, right?
So, it looks like the mirror is positioned to cut the big explosion exactly in half. So this means the larger 'half' of the VFD (with the score and your lives) is closest to the player. When looking at the playfield, you are looking at the actual VFD where your lives are, everything else is either reflected in the mirror, or you are seeing through the mirror.
The side of the VFD with red lightning-looking lines is what you see through the mirror, thus it all looks a little dimmer than the stuff reflected in the mirror. That makes it easier to tell it's on the lower level of the 3D space. You can see this dimming effect well on the players ship as he goes up and down.