The Italians were very wary of box formations, and knew how lethal they could be. Especially B-24s. They knew exactly what range the defensive guns had and how to attack.
They would fly alongside the bomber, which were only doing about 150mph or so, pull up so that the wing obscured the firing angle of the waist gunners, and make an attack from just slightly in front, and sideways.
They knew the guns only had about 300 yards range, but because of the slipstream of air, allied gunners would only open fire at 150 yards (their own observations showed this). They would flip up and swoop over (kind of like a wing-over, if I understand correctly) and aim for the fuselage or wings. They would then split-S very quickly, dive away to safety, and come back. They had over 200kmh speed advantage on the bombers, so it was quite easy to do this very rapidly, and reposition repeatedly, in a short time. Their main problem was firepower. They often ran out of ammo before even running out of fuel (which was also a concern).
They knew that the turn and the split-S would be exposing their full-plan view to the gunners but this was only for a split second so they took that risk.
