Which is complete red herring, given the P-63 was clearly banking inside the turn, so the B-17 was hidden below the cockpit floor in effect, so the blindspot the B-17 was in was nothing to do with the view out of the cockpit!
I've seen a comment from someone involved that the display airboss cleared the fighters into the lower bomber circuit, as had been the pre-show brief if it was clear to do so, which if true, means the airboss either didn't see/expect the B-17 to be there, or more likely cleared the P-51 through and hadn't seen the smaller front profile of the P-63 following it into the lower circuit as well.....