In a case like that the package DM needs to realize that paying the preloaders AND the drivers time and a half (they're going over 8 on road, so extra time in the building is OT even if it's not happening yet) is blowing a huge hole in the DM's cost statement. The smart DM in that case will take a hit for preload PPH and get his/her $70/hour employees (fully loaded wage rate) on the road on time.
The solution is for that DM to understand the operation and force the preload manager to back up the start time to a time they can finish. IE is simply used as a guideline in this case (do the numbers back up what I'm seeing here?).
Then the preload manager needs to run a balanced operation. Running the primary overstaffed and increasing the load area flows works to a point - it takes up the utilization of the loaders. But more of this isn't better. If you blow away the load areas and force everyone to stack (or blow the pieces by and have them fall off the end of the belt) means your loaders will now handle everything twice - and PPH drops to where that manager is on a remediation conference call every day.
Believe me, if the manager knows how to run the operation, the employees don't get overwhelmed and PPH fixes itself just through efficiency.