You have got to boss scrums. The players need to know what you want them to adhere to. Then it is up to them to decide whether they are adhering to that or not.
Coaches do so much research about a referee because they believe refereeing is such a crucial part of the game that the result may hinge on what we say or do. They probably know more about me than I know myself!
If at first you don't succeed, get a bigger hammer.