NFMI has an agreement with Escambia County to not exceed 75 DB at the WEST property Line. To accomplish this restriction, we must know how much sound our Airplane produces and that will dictate how close to the property line you can fly. This is the airplanes distance to the property line and height the plane is in the air.
So if you airplane produces 96 DB at 20 ft on the ground, you can only fly withing 225 ft of the property line, if you were at ground level. If you were 225 ft in the air you could fly up to the property line. So it is a combination of both height and ground distance, to a point at the property boundary, near ground level.
Of course those that are expert in this area, will bring up rightly so, that there are lots of other variables (air density, wind direction, wind speed, just to name a few), and there are, this is meant to be a simple calculator with no outside influences.