[=KAG=Bersrk]

Defencive circle was effective in:

-Jabo missions, prooved in BoB and later in battles on Eastern Front in 41-43.
Group of Bf110\s JaBo, after seeng their alloted target, formed a wide circle, and attacked one after one in shallow dive, then strafing all what survived under the bombs. After job was done, they climb still in circle (defending themself if there were enemy fighters) - and dive away for home, using amazing Bf110 dive abilityes. If that taktics was used properly, losses were really minimal.

-Bomber escort missions. Usually (in early stages of BoB) Bf110's formed defending circle OVER bombers, and moved together with bombers on the course. If RAF fighters choose to attack Bf110's - bombers have clear space to target, and bomb it. If RAF fighters choose to attack bombers - silly choise, keeping in mind a battery of 6 guns, diving on You from behind. All things changed 180*, when Bf110 were ordered to low-speed close-escort, and were tied to bombers. That decesion means a gravesone for many Bf110 crews...

-fighter sweep missions - when Bf110 saw climbing RAF interceptors, they made Abwehrkreuz and, as waited result, most of RAF fighters were busy to attack it, spending ammo and fuel, but usually without any good result. At the moment of german bombers arrive on scene, RAF fighters usually must return to base and land because of fuel/ammo out.

Yes, sometimes there were exeptions, but that exeptions proove a rules.