Only other pics I've found so far are of the nightfighter mounting Jan, and the cannon seems to be in the 'cowled' position, ie, further back, This would make sense on two counts; 1, no forward crewman(?) being hampered by the weapon's receiver, and 2, some of the muzzle flash (much brighter at night)being screened by the fuselage. Not a very strong argument or evidence,I know, but a possible reason for the prortruding muzzle on the ground attack A/C.?