[en] By tailoring the geometry of the upper boundary in turbulent Rayleigh-Bénard convection we manipulate the boundary layer-interior flow interaction, and examine the heat transport using the lattice Boltzmann method. For fixed amplitude and varying boundary wavelength λ, we find that the exponent β in the Nusselt-Rayleigh scaling relation, $Nu-<!--\; ???\; -->1\propto <!--\; ???\; -->R{a}^{\mathrm{\beta <!--\; ??\; -->}}$, is maximized at $\mathrm{\lambda <!--\; ??\; -->}\equiv <!--\; ???\; -->{\mathrm{\lambda <!--\; ??\; -->}}_{max}\approx <!--\; ???\; -->(2\mathrm{\pi <!--\; ??\; -->}{)}^{-<!--\; ???\; -->1}$, but decays to the planar value in both the large ($\mathrm{\lambda <!--\; ??\; -->}\gg <!--\; ???\; -->{\mathrm{\lambda <!--\; ??\; -->}}_{max}$) and small ($\mathrm{\lambda <!--\; ??\; -->}\ll <!--\; ???\; -->{\mathrm{\lambda <!--\; ??\; -->}}_{max}$) wavelength limits. The changes in the exponent originate in the nature of the coupling between the boundary layer and the interior flow. We present a simple scaling argument embodying this coupling, which describes the maximal convective heat flux. (letter)