Previously we have provided a quantitative theory that explains the apparent field dependence observed for chemical shifts in high resolution solids state C-13 nuclear magnetic resonance spectroscopy (where magic angle spinning is combined with high-power H-1 decoupling). We have expanded that theoretical treatment so as to include the effect of homonuclear dipole-dipole couplings among the abundant nuclear spin species, and to the impact of off-resonance rf fields. These differing contributions to the residual linewidths are assessed in a unified theoretical treatment using the Floquet theory for time-dependent Hamiltonians. Some comments are provided as to the circumstances in which the various contributing terms dominate.