  Cosmological observables are particularly sensitive to key ratios of energy
densities and rates, both today and at earlier epochs of the Universe.
Well-known examples include the photon-to-baryon and the matter-to-radiation
ratios. Equally important, though less publicized, are the ratios of
pressure-supported to pressureless matter and the Thomson scattering rate to
the Hubble rate around recombination, both of which observations tightly
constrain. Preserving these key ratios in theories beyond the $\Lambda$
Cold-Dark-Matter ($\Lambda$CDM) model ensures broad concordance with a large
swath of datasets when addressing cosmological tensions. We demonstrate that a
mirror dark sector, reflecting a partial $\mathbb{Z}_2$ symmetry with the
Standard Model, in conjunction with percent level changes to the visible
fine-structure constant and electron mass which represent a
\textit{phenomenological} change to the Thomson scattering rate, maintains
essential cosmological ratios. Incorporating this ratio preserving approach
into a cosmological framework significantly improves agreement to observational
data ($\Delta\chi^2=-35.72$) and completely eliminates the Hubble tension with
a cosmologically inferred $H_0 = 73.80 \pm 1.02$ km/s/Mpc when including the
S$H_0$ES calibration in our analysis. While our approach is certainly
nonminimal, it emphasizes the importance of keeping key ratios constant when
exploring models beyond $\Lambda$CDM.
