Heater hose diameter

Smaller input than output reduces likelihood of waterflow noise which in turn reduces likelihood of costly noise chasing expeditions under warranty, also 1/2" hose and fittings and heater valves saved a couple of pennies per car, and in the auto industry pennies like that make promotions. So why'd they go back to all 5/8" in '73? Who knows? In '70 they were still promoting the inability to lock your keys in a Chrysler Corp car because if you locked it and then closed it, it would unlock; you had to use the key. In '71 they switched to promoting their hot new "keyless locking feature"...you could lock the door and close it without having to use the key!. Different engineers, different marketers, maybe their heater core supplier figured out what was actually causing the noise issues and cut 'em a deal to go back to same-size hoses or???