Why during subsidence inversion, upper layer warms more than lower layer?
I assume that the sentence in the book mainly refers to subsidence as an adiabatic process. This sinking motion has a maximum which is at a height well above the surface, simply for the reason that air flow can not penetrate the earth's surface. Therefore maximum adiabatic heating rates occur well above the surface as well. The precise height where this occurs depends on the height of the planetary boundary layer, which itself depends on many more both adiabatic and diabatic effects.