  Proposed medium-baseline reactor neutrino experiments offer unprecedented
opportunities to probe, at the same time, the mass-mixing parameters which
govern $\nu_e$ oscillations both at short wavelength (delta m^2 and theta_{12})
and at long wavelength (Delta m^2 and theta_{13}), as well as their tiny
interference effects related to the mass hierarchy (i.e., the relative sign of
Delta m^2 and delta m^2). In order to take full advantage of these
opportunities, precision calculations and refined statistical analyses of event
spectra are required. In such a context, we revisit several input ingredients,
including: nucleon recoil in inverse beta decay and its impact on energy
reconstruction and resolution, hierarchy and matter effects in the oscillation
probability, spread of reactor distances, irreducible backgrounds from
geoneutrinos and from far reactors, and degeneracies between energy scale and
spectrum shape uncertainties. We also introduce a continuous parameter alpha,
which interpolates smoothly between normal hierarchy (alpha=+1) and inverted
hierarchy (alpha=-1). The determination of the hierarchy is then transformed
from a test of hypothesis to a parameter estimation, with a sensitivity given
by the distance of the true case (either alpha=+1 or alpha=-1) from the
undecidable case (alpha=0). Numerical experiments are performed for the
specific set up envisaged for the JUNO project, assuming a realistic sample of
O(10^5) reactor events. We find a typical sensitivity of ~2 sigma to the
hierarchy in JUNO, which, however, can be challenged by energy scale and
spectrum shape systematics, whose possible conspiracy effects are investigated.
The prospective accuracy reachable for the other mass-mixing parameters is also
discussed.
