There's some exploitable game mechanic w/ Burst. When targetting a more distant enemy, it's more likely that the intended enemy dies as long as he's in the burst cone. Targetting more distant, a single burst can (and will) mow down 3-4 enemies total. Bursting someone closer, the bullets that miss won't spread to other enemies if they're farther away.
Assuming low CTH, firing rounds at the distance is more effective even if the closer enemy has relatively higher CTH. Fire at 20% CTH with closer enemy at 30% CTH, both die. Fire directly at closer enemy, he barely gets a scratch.