With having worked as a LEO for over 25 yrs now, I have seen that most shooting instances happen with in 21ft. The closer you are to your assailant, the faster you have to aquier your target and make your shots count before he does his or hers.
That's why I advocate dry fire practice at home. I teach the shooting portion of CCW for people who feel they may not qualify for the test.
I tell them to practice in their home with the weapon that they are most likely to carry.
I tell them to make sure the weapon is unloaded, clear and safe. Take all the ammo into another room completely and secure it. Do it while alone so they can practice without disturbance.
I tell them to dress for that time of year and place their carry weapon on them like they plan on carrying.
Pick out a small spot on the wall or item at about 21ft if possible. Then standing comfortable with arms at their side, draw. If they are not able to draw and get at least 1 round off in 2 seconds without the sights leaving that spot, they need to look at how they are carrying and modify it. Then, they need to change/modify how they carry.