[bilky asko]

Thank you Studio7, that was the picture I was looking for this morning when I got 'lost' on Google following too many interesting links (as you do). 

The reflection is not a keyed-element, it is a deliberate layer of the VR environment, over and above the physical set. You could paint the top of the desk 'pink with purple polkadots', and the reflection effect would still be maintained by the VR rendering. It's not relying on any green reflection from within the studio.

It would indeed still be maintained, but you'd not see it, as there'd be nothing keyed out in that position. That is why there is an overlap, as DTV notes. It means that the effect goes right to the edge of the actual acrylic top.

Occasionally in the past, this hasn't always worked quite right, as can be seen in this example below (at the topmost corner of the desk, as the camera looks at it):