I used to relieve the boredom of driving a diesel by opening the throttle as the ammeter drew away from max - unrealistic - also by opening to a square rule - 4mph, 2nd, 9mph, 3rd.
In TRS19 I am getting nagged all the time - rough handling - excessive curve speed etc.
But as to the ammeter setting I have no clue, you need the loco builder to advise, they all behave differently, the Class 66 hits max in setting 2.
I also note that if you are following an AI with an identical consist you need three times the power to keep up, so my method is rubbish.
Any real-life engineers out there?