Wildfire research has made giant progress in the past 30 years. Since the late 1980s, researchers have been making experiments with controlled ignitions at different distances from houses, varying speed and angle of the wind (using big fans, really), and playing into different geometric configurations for the target house.
The present research paper, dated 2018, revisits the 0-5 ft zone. It did find some danger for an ignition source at 5 ft of an outside corner with winds leading straight into the house, and also found that a similar ignition source at a 7-ft distance did not create dangerous temperatures on the walls.
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The conclusion of the study: “with a 5-ft noncombustible zone, the temperature on the wall was continuously below 200°C (potential ignition temperature), except at the corner configuration. Given that the critical temperature is a conservative threshold and that it is not likely that wind blows at the same angle at the corner for a long time, the testing confirms that the current 0–5 ft noncombustible zone recommendation provides a proper noncombustible zone.”