6 Pounder Anti tank Gun - Additional Armour plate

[Rob Abbott]

Hoping someone can help me with this one.
I have my 6Pdr AT gun set up as a single shield version. However the cut out slots on the upper and lower shields are already present and I have a set of the add on armour plate ready to attach.
Despite trawling the available books and manuals however, I still haven't been able to answer a few basic questions:
1. What was the driver for adding the extra plates? I am assuming battle experience and the view that it offered the crew some form of additional protection, possibly against evolving enemy weapons such as shaped charges as the plates are spaced??
2. At what point did the modification first come into service - again based on photographic evidence im assuming autumn/winter 1944?
3. Were British/Canadian guns retro fitted with the equipment or were the additional shields only fitted to newer equipment as it was issued or guns replaced?
4. How effective was it? There is considerable extra weight on a gun which already takes a fair amount of strength for the crew to manhandle. Was it a justifiable improvement in the eyes of those using it?

Sorry to everyone for the number of questions but like everything 6 Pounder related, information on this seems difficult to come by !

Any thoughts, help and information greatly appreciated.
Thanks
Rob