  We prove that the stabilizer fidelity is multiplicative for the tensor
product of an arbitrary number of single-qubit states. We also show that the
relative entropy of magic becomes additive if all the single-qubit states but
one belong to a symmetry axis of the stabilizer octahedron. We extend the
latter results to include all the $\alpha$-$z$ R\'enyi relative entropy of
magic. This allows us to identify a continuous set of magic monotones that are
additive for single-qubit states. We also show that all the monotones mentioned
above are additive for several standard two and three-qubit states subject to
depolarizing noise. Finally, we obtain closed-form expressions for several
states and tighter lower bounds for the overhead of probabilistic one-shot
magic state distillation.
