There is of course a lot of debate and discussion on how/why this terrible incident occurred. The comment reference the Air Boss allowing the fighters to use the bomber levels "if everything looked clear" is surprising to me.
A lot of focus is on the few seconds prior to impact but I wonder if it all began to unravel much earlier, when the fighters (P51 P51 P63) were still heading south-ish and the bomber groups would have been more or less directly ahead and crossing right to left. If P63 saw the second bomber group and assumed it was the lead group his SA has gone and to all intents and purposes the airspace to his right and below "must be clear" as he tips in fast and wide.
I'd like to see the ADSB overlay for that second little group of bombers and how that fits in with where the fighters (P51 P51 P63) were.
I have done some flying but my thought process here stems from a mis-ident as a controller in a very busy visual circuit. It led me to make a mistake where the aircraft I was seeing downwind was not the one that had just called downwind.