FBI - Subject sees light and distracts from Officers position. It can also work as a spotlight for searching and navigating (Technique - flashlight held out and high in off hand).
Neck Index - The control position. Can create shadow and backsplash off pistol and clothing (Technique - flashlight held at neck index in off hand).
Harries - Most useful for firearm stabilization and control. (Technique - flashlight held underneath shooting hand).