Remember, constructive placement costs you double. Cars parked on railroad owned track awaiting placement deny you the use of that track whether those cars are system owned or privately owned. Since denial of this track is caused by a customer driven problem, you must be compensated for it. What's more, you have to absorb the crew cost for the second car placement onto the customer's track. Under these circumstances, demurrage on privately owned cars constructively laced on railroad owned track is a bargain compared to switching charges for cars placed on the cusotmer's track and then moved within the customer's facilit.
Demurrage has nothing to do with car-hire, and everything to do with use of railroad resources.
You can find out why you had to CP the cars, and work to eliminate the cause. If a plant slowdown and decrease in raw materials used is behind it, you can go bactk through the chain to slow the order process. If a shortage of storage space to supply a growing process is at fault, you can work with your customer to extend the track or build more inventory handling capacity. Here's another reason not to couple casr-hire management ot an aggressive demurrage tariff. You'll never make these kinds of tariffs stick with your best customers, and trying to enforce themwith your second-best will eat at the stomach lining of your office staff and ultimately lose you the business.