How do you arrive at the "within 5 feet" conclusion? What does that have to do with it. If you think the fielder could have gotten to the ball then the runner is out. Don't start saying "5 feet". What about 5 1/2 feet? Would that be ok? I don't take a ruler on the field with me.
You can also apply the "common sense and fair play" ruling which is the runner is not out once the ball passes an infielder. If the 3rd baseman misses a ball under his glove and it hits the runner you are penalizing the runner and rewarding the 3rd baseman who just missed the ball. The fielder screwed up by missing the ball. Don't penalize the runner! I know what the rule book says and that's how I umpire. But there is a good argument for not penalizing the wrong team. And it's easy to justify in an arguement..."in my judgement your shortstop could not have made a play on the ball". End of discussion. I think you get more heat if you call the runner out. Just my opinion. But I'm wrong 99% of the time according to the fans so what do I know....