While the minimum predefined distance is 2 meters, you may define an arm's reach distance which should be at least 500 mm (50 cm or 1.64 f). After measuring the distance between your hand/wrist holding a smart phone and your eyes, you input the distance in "Arm's Reach Distance" in Settings, then this distance will appear in the Predefined Distances.
To identify nearsightedness symptoms, the test distance should be at least 2-meter which is longer than arm's reach. Since generally an arm's reach distance is much shoter than 2-meter, this testing mode is good only for casual self-diagnosis for example when you are on a train, and the test result is inaccurate and unreliable. It may be easier to use Self-diagnosis with a Mirror.