How does the engineer/driver know when to pull forward so the next car can load at a tipple?
How does he/she move the proper distance to insure the car is fully loaded?

I noted a comment about how unrealistically fast the coal loading process is. A 20 car consist takes about 12 minutes at an Mgsapper 4 track tipple. The loading method is a drop down trough which is retracted between card. The process is slow and boring but probably approaches reality more then others.