To Fearless' point. Flying formation (and there are much better experts here than me), you focus on your lead. There is nothing else in your world. That's why when the Thunderbirds did their loop into the ground a bunch of years ago, the 5 (?) airplanes all impacted within spitting distance. The wingmen were following lead as they were supposed to. Lead messed up and they died. In this situation, the failure seems to have been that the P-63 DIDN'T do a good job of following the aircraft he was following (formating on). He absolutely should not have been looking for the B-17. He should have been locked on the aircraft he was following.