When you said "string lining" I thought you were referring to the phenomena that happens to a train when it has too much tonnage on the rear for very light cars (like intermodal) up front going into a sharp curve. Placement-in-train rules are in-part written from the real world experience of doing things like that. That happened in Fostoria, OH earlier this year on the connection from the C&O line to Columbus to the B&O Chicago main towards Willard, right after Harrison took over and started implementing massively long trains. It also happened about 40 years ago in Akron, which, I'm guessing, might have led to the original rule about trailing tonnage behind intermodal cars.