Aggregate Jobs should favor largest trucks

Many times when I see the message that my trucks are extremely busy, its usually due to aggregate (rock, dirt from mines). However, the largest haul trucks are sitting around while the smaller trucks are over worked. I think this is because as soon as a silo starts to fill, a job is created for the smaller truck capacity vs the larger (my guess). Instead jobs should focus on largest possible haul first and if none available move to smaller.