In the US you have different headlight standards than we do in most of the rest of the world, you have the SAE standard and we have the ECE standard so I expect your airheads are shipped with a different headlight setup. According to Wiki your SAE standard allows for more glare than the ECE system.
Anyway, as far as I am aware the metal bowl is simply a glare shield, it does not have a polished surface and I cant see how it could possibly improve the light output. I remove the shields from my lights, IMO it increases the lumen output and my visibility. Half the cars on the road are running headlights that dazzle me, Id rather dazzle them a little than merge into invisibility with my old H4's but each to their own.
Heres a wiki quote regarding the shields
The traditional European method of achieving low and high beam from a single bulb involves two filaments along the axis of the reflector. The high beam filament is on the focal point, while the low beam filament is approximately 1 cm forward of the focal point and 3 mm above the axis. Below the low beam filament is a cup-shaped shield (called a "Graves Shield") spanning an arc of 165°. When the low beam filament is illuminated, this shield casts a shadow on the corresponding lower area of the reflector, blocking downward light rays that would otherwise strike the reflector and be cast above the horizon. The bulb is rotated (or "clocked") within the headlamp to position the Graves Shield so as to allow light to strike a 15° wedge of the lower half of the reflector. This is used to create the upsweep or upstep characteristic of ECE low beam light distributions. The bulb's rotative position within the reflector depends on the type of beam pattern to be produced and the traffic directionality of the market for which the headlamp is intended.