  Two-temperature advection dominated accretion flow (ADAF) or hot ion tori
(HIT) models help explain low luminosity stellar and galactic accreting sources
and may complement observational support for black holes in nature. But low
radiative efficiencies demand that ions receive a fraction $\eta \gsim 99%$ of
energy dissipated in the turbulent accretion. The $\eta$ depends on the ratio
of particle to magnetic pressure. If compressive modes of dissipation, like
magnetic mirroring, dominate incompressible modes, then even when the pressure
ratio is O(1), the required large $\eta$ can be attained. However the relative
importance of compressive vs. incompressible modes is hard to estimate. The
larger up in the turbulent cascade, the more compressible the turbulence. The
relevant length scale for particle energization can be determined by equating
the dominant eddy turnover time to the time for which an energy equal to that
in the turbulence can be drained. Based on the large scales resulting from this
estimate, it is suggested that compressive mirroring may be important. Also,
regardless of the precise $\eta$ or dissipation mechanism, non-thermal protons
seem natural in two- temperature discs because all dissipation mechanisms, and
the use of an isotopic pressure, require wave-particle resonances that operate
only on a subset of the particles. Finally, it is briefly mentioned how
mirroring may help to generate an ADAF or HIT in the first place.
