Following up from another thread, excluding reflections and what not, a plane at 75 feet should be 16x louder than the same plane with the same throttle setting

Following up from another thread, excluding reflections and what not, a plane at 75 feet should be 16x louder than the same plane with the same throttle settings at 300 feet. Sound follows the inverse square rule, where a change in distance of X reduces the perceived noise to 1/x^2. Since 300/75 = 4, you get a factor of 16 in perceived difference. Yikes.