This is due to your height above average terrain. When the FCC processes your application, they look at your location's elevation and antenna height above ground, then they make measurements at multiple points along 8 equally spaced radials to determine the elevations in each direction. The average heights of the points of these radials make up your height above average terrain (HAAT). If your HAAT is greater than 30 meters, your effective radiated power (ERP) is reduced to the level that is necessary to produce a service contour of 5.6 kilometers.
LPFM technical operations
LPFM station planning and construction