  We re-examine the question of quantum oscillations from surface Fermi arcs
and chiral modes in Weyl semimetals. By introducing two tools - semiclassical
phase-space quantization and a numerical implementation of a layered
construction of Weyl semimetals - we discover several important generalizations
to previous conclusions that were implicitly tailored to the special case of
identical Fermi arcs on top and bottom surfaces. We show that the phase-space
quantization picture fixes an ambiguity in the previously utilized energy-time
quantization approach and correctly reproduces the numerically calculated
quantum oscillations for generic Weyl semimetals with distinctly curved Fermi
arcs on the two surfaces. Based on these methods, we identify a 'magic'
magnetic-field angle where quantum oscillations become independent of sample
thickness, with striking experimental implications. We also analyze the
stability of these quantum oscillations to disorder, and show that the
high-field oscillations are expected to persist in samples whose thickness
parametrically exceeds the quantum mean free path.
