Why The lower atmosphere's density and moisture decrease with height, so VHF/UHF signals refract slightly downward and bend around the curve of the Earth a bit more than light does. Propagation engineers model this by pretending the Earth has 4/3 its true radius; since horizon distance scales as the square root of the radius, the radio horizon is sqrt(4/3) = 1.155 times the geometric one, about 15 percent farther.
Watch out The choice saying they are about the same would be true only if radio waves traveled in perfectly straight lines with no tropospheric refraction, and 50 percent farther overstates the bending by a wide margin.
4/3 Earth radius, sqrt(4/3) = 1.15, so radio sees about 15 percent farther than the eye.