An extensive investigation of the equilibrium sites of H in p-type silicon has been performed in order to clarify the inffluence of the specific impurity on the geometry of the silicon-hydrogen-acceptor complexes. Previous studies focused onto the B and Al cases have been extended to the isovalent acceptors Ga and In, making clear the relevance of the impurity atomic size. The on-axis BC site is shown to be a marginal equilibrium position, which evolves toward an off-axis position as soon as the acceptor size exceeds that of B. A novel H metastable site has been estimated, only in Si:In, at the AB-In site, thus suggesting a dependence of H equilibrium sites on the full chemistry of the impurity. These results account well for far-infrared measurements in Si:Al and Si:Ga, as well as for perturbed \ensuremath{\gamma}\ensuremath{\gamma} angular correlation results in Si:In.