Look at the location of the pilot’s eyes and then the leading edge of the wing. Then think about the length and width of a B-17. Now think about what the pilot would see as he gained altitude, prior to flying roughly level to the impact point. The B-17 would most certainly be visible from the cockpit of either a P-51 or a P-63.
You are completely wrong. Have you ever flown in a B-17? Have your ever flown in a prop fighter aircraft? Didn't think so.
I was a flight instructor in the Navy and we practiced breakups and rendezvous all the time - day, night and using NVDs
Losing sight of the lead happens - especially when coming in at too acute an angle and the pilot has to increase angle of bank to get into position - not a good feeling.