Lowest skill is normally thought to be zero. The difference between 0 and 0.01 will not be noticeable. You might just be able to tell the difference between 0 and 0.1.
Skill doesn't just affect the AI's ability to shoot straight, it also affects their ability to detect you and their rate of fire. In other words, to achieve the effect you want, 0 skill may not be the optimum number. 0.2, for example, might actually be more fun. Experiment.
You can also use addon units with HD (high dispersion) weapons for longer firefights.