A lot of different techniques here. There's the "in-line" idea. The mic is always pointed straight at the mouth. Soft singing the mic is right next to the mouth. Screaming, the mic gets pulled away from the mouth 6-18 inches. The louder the scream, the farther from the mouth. Then there's the angled-mic idea. Again, soft singing, the mic is right next to the mouth, and pointed right at the mouth. Screaming, the mic is angled so it is no longer pointing straight into the mouth. The mic now points more up toward the ceiling. The singing is now moving across the front of the mic, rather than directly into the mic. The mic is then moved either downward, or outward to control volume. Whatever way is used, the exact amount the mic is moved must be learned by experience by the singer. And, it depends, a lot, on the response of the microphone. Every mic is different... every singer is different. Ya just gotta learn by doing.