The basic idea is simple: add different ammo types that change the arcing range which will hence affect the dps and alpha. For instance their could be another ammo decreasing the arc range to 5km, which then would increase the dps by, say 5-10% or decrease the base dps by 5-10%, with perhaps another ammo with no arcing distance at all, but increases dps to 10-20% or vice versa.