I think swarming behavior works like this:
All of the fighters (w/Swarming) launched from a particular capital ship form into one group. The fighters somehow "elect" a lead ship. All of the other fighters will simply try to stay close to/follow the lead ship; they won't try to actually shoot at the enemy unless they find themselves very close, not even if they're carrying missiles/railguns, or if they're being fired upon. The lead ship, however, will hunt down it's target relentlessly, using whatever it has at it's disposal. If you were to destroy the lead ship, another fighter would be chosen as a successor, until there were no more fighters left. If, however, the following fighters are being attacked, it has no bearing whatsoever upon the lead ship.
When fighting Pirate Carriers, I've noticed that I can string the fighters out. The fighters would form a crescent, with the lead ship at one end, trying to get to you, and the rest of the fighters forming the rest of the crescent, trying to get to the lead ship. If I have railguns or FPC's, the rest of this crescent becomes an obscenely easy target.
Swarming behavior will, no doubt, work against AI enemies, as they don't try to circle around their opponents. Against a player, it simply isn't a great challenge.
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"Trust me, this'll work..." - Me.
"WARPCORE BREACH IN 10 SECONDS." - Computer.
"... Of course, I could be wrong..." - Me.