With the CE test the reverse is often one of the bigger challenges. But remember that, if it starts going wrong, take a shunt and make it count.
If you picture the “A” cones (the ones in front of you when you start) and draw an imaginary line between them and then fully across the reversing area, that is the limit of your shunt. A shunt will generate a driving fault - whether its a 10 foot shunt or a 100 foot shunt. So the advice is to use all the room available to you - - - exactly the same as in the real world.
Hope this helps, Pete 