@Federico While the P-63 with its rear-engine configuration probably has relatively good visibility (for a WW2 fighter) in the forward direction, i.e. along its velocity vector, the relative velocity between it and the aircraft being closed on could easily have been in a very different direction. Hence the danger of ever turning "belly-toward" another aircraft. I find the ideas in this "Probably Cause" video starting at 22:05 youtu.be/QunMRwNzr_c?t=1324 to be thought-provoking.

@Federico ("Probable")