So... This is why zeroing at a very short range is SAID to work as a substitute for zeroing at a longer range.
But the problem is this - at 13yrds, if you're off by 1/4", simply because you've mis-estimated your optic height, or because you only shot 3 shots and didn't properly represent the ACTUAL center of your group, or any other reason, then when you get to 100yrds, you'll be off by 2". Take a shot at 200yrds, and you'll be off by 4"...
Shooting at short ranges will work well enough to get you on paper at 100yrds, but it should never be exclusively used as a substitute for firing groups at range.