  Within a covariant perturbative field-theoretical approach, the wave-packet
modified neutrino propagator is expressed as an asymptotic expansion in powers
of dimensionless Lorentz- and rotation-invariant variables. The expansion is
valid at high energies and short but macroscopic space-time distances between
the vertices of the proper Feynman macrodiagram. In terms of duality between
the propagator and the effective neutrino wave packet, at short times and
distances, neutrinos are deeply virtual and move quasiclassically. In the
lowest-order approximation, this leads to the classical inverse-square
dependence of the modulus squared flavor transition amplitude and related
neutrino-induced event rate from distance $L$ between the source and detector,
and the above-mentioned asymptotics results in the corrections to the classical
behavior represented by powers of $L^2$. This is very different from the
long-baseline regime, where similar corrections are given by an asymptotic
expansion in inverse powers of $L^2$. However, in both short- and long-baseline
regimes, the main corrections lead to a decrease in number of neutrino events.
