I'd continue practicing at 21 feet. I figure if you master 21 feet (or more), there's no question you'll be able to accurately hit the center of your target at 10 feet.
May I suggest Gabe Suarez's new DVD on Close Quarters Gun Fighting", for one. Things are not the same at 21 ft. as they are real close. Neither are the skills and tactics you'll need. You may need to use these skills before you can even draw your weapon, not to mention shooting at spittin' distance.
If you were correct, there wouldn't be a number of good tapes by excellent instructors dealing with extreme close quarters fighting.