  The interaction of binary black hole mergers with their environments can be
studied using numerical relativity simulations. These start only a short finite
time before merger, at which point appropriate initial conditions must be
imposed. A key task is therefore to identify the configuration that is
appropriate for the binary and its environment at this stage of the evolution.
In this work we study the behaviour of wave dark matter around equal mass black
hole binaries, finding that there is a preferred, quasi-stationary profile that
persists and grows over multiple orbits, in contrast to heavier mass dark
matter where any overdensity tends to be dispersed by the binary motion. Whilst
different initial configurations converge to the preferred quasi-stationary one
after several orbits, unwanted transient oscillations are generated in the
process, which may impact on the signal in short simulation runs. We also point
out that naively superimposing the matter onto a circular binary results in
artificially eccentric orbits due to the matter backreaction, which is an
effect of the initial conditions and not a signature of dark matter. We discuss
the further work required so that comparison of waveforms obtained with
environments to vacuum cases can be done in a meaningful way.
