really? well guess all them 109 vs B-17 gun footage film when they were accurately hitting the engines were just lucky shots?
I doubt very much they would concentrate on hitting a B-17's upper/middle fuse. goes for any fighter attacking heavy bombers.
For most pilots, yes, a lot of it would of been luck. There were a lot of other factors. Ignoring pilot skill, things affecting the likelihood of hitting a target include the aircraft they were flying and its armament, the aspect and speed of the target, the altitude they were operating at, the range they opened and closed fire, the relative angle and rate of closure.
The gun camera footage kept by Luftwaffe operational research groups was primarily that of successful attacks.
Working off the US assessment of German operational gun cam records, at 100 m, the likelyhood of a German fighter observably hitting a B-24/B-17 on any single pass (front, sides, rear) was about 40%. Rear attacks were notably more likely to result in hits, but even then, single shot hit probability of hitting a heavy bomber target was just 25%.
Of these close in attacks, around one third were considered "good" (ie concentrated on target, within the limits of typical dispersion) while the other two thirds wandered over the target.
At 100 m, a rear aimed pass would typically result in 18-20 rounds observed as hitting the target - typically these are 20/30 mm HE/API hits, as pure AP and smaller rounds (7.9 and 13 mm) were much harder to observe. A nose-on pass would typically put 5 20/30 mm observable rounds on target at 100 m.
The Luftwaffe estimated that it usually required 18 20mm mine rounds or 4 30 mm mine rounds to cripple or kill a US heavy bomber.
At a more usual firing distance of 500 m, the likelyhood of a fighter hitting the target on any single pass drops well below 10%. Notably though, the number of observed rounds hitting drops significantly, around 8 per pass from the rear and just two per pass from the front.