One simplistic approach can be by making the targeting fuzzy. Instead of directly targeting a location, choose a random location within a given radius range. Ideally you are projecting a point you are targeting based on velocity and heading of both your missile and the target, and then applying the fuzzieness.
Having a minimum radius on that fuzziness can decrease the maximum accuracy. So that random location is never on target directly if you don't want it to be.
You could then also shrink how fuzzy that is the closer you get just by shrinking the min/max radius, so that you are not missing the target based on fuzzieness.
Obviously the more fuzzieness you have, the more likely that missile is going to miss that target.