According to the linked Preliminary Report:
"There were no altitude deconflictions briefed before the flight or while the airplanes were in the air. When the fighter formation approached the flying display area, the P-63F was in a left bank and it collided with the left side of the B-17G, just aft of the wing section."
Which I understand to mean that the Fighters and Bombers were never separated vertically.
That does not look like safe planning.
IB