It’s called “push-pull mode”. The locomotive always stays at one end and a cab car at the other. This way reversing the train at the end of the line doesn’t mean using a wye. The operator merely goes from the cab car to the locomotive or vice versa. On this part of Metro-North, the locomotive always runs at the north end of the train and the cab car at the south end.
I know that there is a certain practice of having a loco at either end....I do have a large post war lionel collection. that makes me an expert in......nothing.