Clip, Rifle, Double - Dimensions

[derk derin]

The weapons mount hold a spare Bren gun and a spare service rifle. On the floor in front of the battery is a double gun butt holder where the butts fit into. The muzzle ends of the weapons fit into the top clips. Originally they were rubber straps that secured the weapons in but as they failed the web straps were fitted to the mount.
Here is the top part of the mount shown on my carrier;
What I would like to know is if there was anything intended to be stowed in the tray. I have a spare Bren mag sitting in it but curious if it was an actual spot for a specific piece of equipment?