Here's a useful article:
http://www.combatsim.com/htm/aug99/fighter-tactic1.htm This one seems particularly relavant...
THE SWOOPER
Lead Squadron of Group, Any Combat Wing
TACTICS DESCRIPTION
In the diagram above, the single-engine aircraft makes a diving attack from 10 o'clock, high, swooping down under the squadron. Seldom is the fighter closer to the Fortress squadron than 500 yards, and in this type of attack the fighter comes down from an angle of between 30 and 40 degrees, without rolling over. The fighter pulls out of the dive when clear of the squadron.
IMPORTANT: This type of diving attack can be and often is made under the high and low squadrons, as follows:
(1) Under low squadron, from any position between 6 to 12 o'clock, high.
(2) Under the high squadron, from any position between 12 to 3 o'clock, high.
The diving attack under the lead squadron is often made from any position between 9 to 1 o'clock, high.
VARIATION
While in the majority of these swooping attacks the figher goes under the squadron formation, sometimes it goes over the formation. If the combat formation is bad, the fighter may dive and go through the formation, i.e., between the lead and high squadrons or, if diving from the 12 to 3 o'clock positions, between the lead and low squadrons. Almost invariably, when the fighter dives and pulls up over the formation, the pull-up is over the high squadron.
TACTICS LESSON
Diving attacks with deflection are what we like. The fighter is at a disadvantage. He has a hard shot and can get in only a short burst. Gunners have plenty of time to shoot him down.That said, I find that a 90º deflection diving attack is what works best for me vs B-17's also...