To get a 3:1 lighting ratio with two lights of identical power, when using on-axis fill light (i.e. fill light placed right NEXT TO the camera's angle of view and aimed straight ahead at the subject), the fill light needs to be 1 full f/stop lower in exposure value at the subject than the main light's exposure value at the subject. So, for example, with two identical flash units at the same exact power, the traditional method is to have the fill light farther away from the subject than the main light. For example, with two identical lights, there's a fascinating "one-stop difference" series of main light distances and fill light distances: 1.4 feet, 2.0 feet, 2.8 feet, 4 feet, 5.6 feet, 8 feet, 11 feet, 16 feet, 22 feet. Imagine that!!!! If the main light is at 4 feet from the subject, the fill light of the same power would need to be at 5.6 feet from the subject to give a 3:1 lighting ratio.
In actual use, it's pretty common to move the fill light back, farther away, than the main light to subject distance.