  Maximizing the ratio between Kitaev and residual Heisenberg interactions is a
major goal in nowadays research on Kitaev-Heisenberg quantum magnets. Here we
investigate Kitaev-Heisenberg exchange in a recently discovered crystalline
phase of RuCl$_3$ under presure -- it displays unusually high symmetry, with
only one type of Ru-Ru links, and uniform Ru-Cl-Ru bond angles of
$\approx$93$^{\circ}$. By quantum chemical calculations in this particular
honeycomb-lattice setting we find a very small $J$, which yields a $K/J$ ratio
as large as $\sim$100. Interestingly, we also find that this is associated with
vanishingly small $d$-shell trigonal splittings, i.\,e., minimal departure from
ideal $j_{\mathrm{eff}}\!=\!1/2$ moments. This reconfirms RuCl$_3$ as a most
promising platform for materializing the much sought-after Kitaev spin-liquid
phase and stimulates further experiments under strain and pressure.
