  We revisit the amplitude-based derivation of gravitational waveform for the
scattering of two scalar black holes at subleading post-Minkowskian (PM) order.
We take an eikonal-inspired approach to the two-massive-particle cut needed in
the KMOC framework, as highlighted in arXiv:2308.02125, and show that its
effect is to implement a simple change of frame. This clarifies one of the
points raised in arXiv:2309.14925 when comparing with the post-Newtonian (PN)
results. We then provide an explicit PM expression for the waveform in the soft
limit, $\omega\to0$, including the first non-universal, $\omega\log\omega$,
contribution. Focusing on this regime, we show that the small-velocity limit of
our result agrees with the soft limit of the PN waveform of arXiv:2309.14925,
provided that the two quantities are written in the same asymptotic frame.
Performing the BMS supertranslation that, as discussed in arXiv:2201.11607, is
responsible for the $\mathcal O(G)$ static contribution to the asymptotic field
employed in the PN literature, we find agreement between the amplitude-based
and the PN soft waveform up to and including $G^3/c^5$ order.
