  We perform a Bohmian-trajectory analysis of high-order harmonic generation
(HHG), focusing on the fact that typical HHG spectra are best reproduced by the
Bohmian trajectory starting at the innermost part of the core [Phys. Rev. A
\textbf{88}, 023415 (2013)]. Using ensemble averages around this central
trajectory, we show that, for the high-plateau and cutoff harmonics, small
ensembles of Bohmian trajectories are sufficient for a quantitative agreement
with the numerical solution of the time-dependent Schr\"odinger equation
(TDSE), while larger ensembles are necessary in the low-plateau region.
Furthermore, we relate the Bohmian trajectories to the "short" and "long"
trajectories encountered in the Strong-Field Approximation (SFA), and show that
the time-frequency maps from the central Bohmian trajectory overestimate the
contributions of the long SFA trajectory, in comparison to the outcome of the
TDSE computations. We also discuss how the time-frequency profile of the
central trajectory may be influenced nonlocally by degrading the wave-packet
propagation far from the core.
