There are three factors in an overshoot: 1) closure, 2) angles, and 3) timing.
The whole point is to put your opponent into a situation where it's not possible for him to "square" the corner to get on your six forcing him to fly past your flight path. How you do this varies but all three of these factors come into play to some degree. Usually, one will be the predominant factor.
For instance a Zeke is at 200 mph and a 109 dives toward it from 5k above. The 109 is screaming along at 450mph trying not to compress. In this case closure is going to do 99% of the work for Zeke and all he has to do is dodge the 109's shot with a momentary break turn and the 109 WILL overshoot.
Now, take the same two aircraft but this time they are co-alt with similar e. The 109 is 1k on the Zeke's tail and slowly closing. Since the Zeke can easily out turn a 109 he waits until the 109 opens fire and then breaks into him. The 109 cannot "square" the corner and overshoots. In this case angles are doing 50% of the work and timing the other 50%. Timing becomes important because if the Zeke breaks too soon the 109 will simply high yo-yo and be right back on him. By waiting until the last second the Zeke makes sure the 109 is committed and is unable to pull up until after the overshoot has occured.
Now, take the example you're really asking about. Instead of very different aircraft consider two similar ones, in this case let's say an F6F and F4U. Again, they are co-alt and similar e with the F6F firmly in the driver's seat with no closure and is trying to pick the F4U apart piece by piece. Since both airplanes have the similar performance this is a very difficult spot and the F4U is going to lose unless he does something drastic. A break turn doesn't help because the F6 can do a lazy high yo-yo and there is no significant difference in speed and so they both have comparable turn radius. The last ditch effort is to break, chop the throttle, drop some flap and, as I have cleverly selected the F4U for this example, drop the gear. The F6F easily sees the break turn but doesn't realize the F4U is rapidly decelerating and his 0 closure all of a sudden becomes 150mph of closure and an unavoidable overshoot. Once the F6F crosses the F4U's flight path the Corsair pops his wheels up, slams his throttle forward, hits wep and reverses to a position now on the F6F's tail (or is hopefully at least neutral).
So, the moral of the story is that you need some combination of closure, angles and timing to create an overshoot. If you don't have closure chop throttle and create it.
