In the case of a live target what may also be considered is the lethal shock radius. I now a .22 does have a much larger radius but whether it is really that much more than a .177 at these sub 12 limits needs to be investigated.
I honsetly wish that the .22 had a none FAC limit of 17 ft.lbs. It would have made a lot of difference to the accuracy within the short air rifle ranges without being " particulary dangerous " as defined by law.

A.G