With the apparent large difference in speed, it seems like the B-17 should’ve been easily visible to the P-63 until very shortly before the collision, given that the P-63 was in a hard turn. Makes me wonder if the P-63 pilot was perhaps looking ahead and toward the inside of the turn, looking for the aircraft he was following or something, and just didn’t see the B-17 or misjudged the separation and thought he would turn inside of it.