My CCL instructor ran a drill that emphasized how quickly an assailant can be on you in the time it takes you to draw from concealment and fire with some accuracy. 21ft was as close as you'd want someone to get. Put a bat in their hands or a projectile they can throw and it makes the distance greater. While many subscribe to 10ft-15ft practice at the range, the reality is, they may need far more than that in a real life situation. Personally I shoot 15ft, 25ft, and 50ft every trip to the range to be as prepared as possible.