Air traffic controllers often ask pilots to report a certain number of miles from downwind, base, and so on. But where exactly is the controller asking you to report from?
Generally, the answer is the requested number of miles from the next point. So if a controller says, “report three mile left base,” he or she expects you to report three miles prior to turning final on the base leg. That goes for left or right base, final (just the distance from the runway generally), and others.