I think, generally speaking, all but the most experienced pilots attacking a US combat box are going to fire at whatever fills their sights. My point was that a B-24 seems to have been less likely to survive a cannon shell to the wing as a B-17, due to the design of the airfoil. I'm not sure how widespread targeting of specific components was, but I guess it wasn't all that common.
Continuing with the original theme of the thread, German bomber such as the He111, Ju88 and Dornier 17/215/217 suffered a handicap in the layout of crew accommodation, which clustered the entire crew together in the nose. One near-miss from flak or good burst from a fighter could potentially incapacitate several, if not all of the crew, immediately rendering the bomber finished. Again, I don't believe this was deliberately exploited by RAF fighters in the BoB, but pilots certainly knew that attacking from ahead exposed them to less defensive fire, increasing the risk for bomber crews. As a secondary disadvantage, the clustering of the crew also restricted the placement of defensive armament, and coupled with the German aversion to the use of turrets (except in the Do217), limited the arcs of fire that could be effectively covered, and also reduced available fire power, as guns on the bombers mentioned were usually in single flexible mounts anyway.
