Sizing the Lego Roverbot

As we have noticed the yellow area is largest when the Roverbot's sides are visible by the camera and smallest when viewed from the front or back. We can use the COG module to tell us more about the size of this yellow area. By selecting a bounding box that covers 90% of the detected yellow are we can be sure that we have a good relative approximation of the RCX brick. The COG_AREA will be smaller than when the RCX brick is pointed directly away or towards the camera and larger when the left or right sides are showing.

The following images show the bounding box overlaid on the detected yellow Roverbot.

But how do we know how small the COG_AREA should be when the Roverbot is orientated towards the camera?