I believe if you start you tank away from the direction your pulling from you can help this some, but I believe the setting your looking for is in the melee section.
Rich (BB code):
[Melee]
AssistAt=99
MeleeOn=1
FaceMobOn=1
MeleeDistance=75
StickHow=Loose
AutoFireOn=0
UseMQ2Melee=1
If you make this number smaller they should engage at less distance from camp.