  Recently, Rodenburg et al (2014 New J. Phys. 16 033020) presented an approach
for simulating propagation over a long path of uniformly distributed
Kolmogorov-spectrum turbulence by means of a compact laboratory arrangement
that used two carefully placed and controlled spatial light modulators. We show
that their simulation approach mimics the behavior of plane-wave propagation,
rather than general beam-wave propagation. Thus, the regime in which their
orbital angular momentum (OAM) cross-talk results accurately represent the
behavior to be expected in horizontal-path propagation through turbulence may
be limited to collimated-beam OAM modes whose diameters are sufficient that
turbulence-induced beam spread is negligible.
