At the most platforms at stations it is always required in TS2015 to stop at the end of a platform. This is usually the most common place to stop a train. In practice a passenger trains always stops as close as possible to the main exit / main entrance for passengers have rapid access to the train and exits of the station. Passengers will always hold up close to the exits, stairways and elevators.
A Flying Scotsman stops in TS2015 on the right spot.
You have to be aware of the wishes of the passengers. Most passengers does not walk too far from the main exit and they always try to poses a chair close to the door, facing the driving direction and depending the left or right hand traffic either on the left or right side of the train and mostly direct behind the driver. If the coach has compartments. the passenger always find an empty compartment. close the door behind it and hopes no one will enter to gain silence and rest. The passenger experiences this spot as the most comfortable in the whole train.
Every Railroad company does have their own regulations for a specific train to stop at a determined position along the platform. This is usually a sign post wtih a number shown.
The number is equal to the amount of coaches the train consists. The engine or first EMU or DMU has to stop at about 1 yard for that stopping sign accordingly the correct train length or amount of coaches. The position of the doors now is the most economical position for train and passengers to embark / disembark.
Short platforms, long trains.
There are occasions a train is too large for a certain platform to stop at. When a train is too large then you have to act as follow;
Pass slowly the platform with your engine completely until the first door of the coach stops just at the edge of the platform head.