  Denote by $\mathcal{N}\!\mathcal{A}$ and $\mathcal{MA}$ the ideals of
null-additive and meager-additive subsets of $2^\omega$, respectively. We prove
in ZFC that
$\mathrm{add}(\mathcal{N}\!\mathcal{A})=\mathrm{non}(\mathcal{N}\!\mathcal{A})$
and introduce a new (Polish) relational system to reformulate Bartoszy\'nski's
and Judah's characterization of the uniformity of $\mathcal{MA}$, which is
helpful to understand the combinatorics of $\mathcal{MA}$ and to prove
consistency results. As for the latter, we prove that
$\mathrm{cov}(\mathcal{MA})<\mathfrak{c}$ (even
$\mathrm{cov}(\mathcal{MA})<\mathrm{non}(\mathcal{N})$) is consistent with ZFC,
as well as several constellations of Cicho\'n's diagram with
$\mathrm{non}(\mathcal{N}\!\mathcal{A})$, $\mathrm{non}(\mathcal{MA})$ and
$\mathrm{add}(\mathcal{SN})$, which include
$\mathrm{non}(\mathcal{N}\!\mathcal{A})<\mathfrak{b}<
\mathrm{non}(\mathcal{MA})$ and $\mathfrak{b}<
\mathrm{add}(\mathcal{SN})<\mathrm{cov}(\mathcal{M})<\mathfrak{d}=\mathfrak{c}$.
