I actually made an edit to a similar section of text in the paper - I'm not sure I understand this description of the `alias_threshold` parameter, and in the paper I instead wrote:
```
  \code{alias\_threshold} sets a maximum amount of real space
  aliasing that is allowed, an effect caused by the periodic nature of
  DFTs.  DFTs implicitly use periodic boundary conditions, and a
  profile specified on a finite grid in Fourier space corresponds to a
  real space image that will have some overlap with the neighbouring
  (aliased) copies of the real space profile.  As the step size in $k$
  increases, the spacing between neighbouring aliases in real space
  decreases, increasing the amount of overlapping flux.
\code{alias\_threshold} is used to set an
  appropriate step size in $k$ to allow at most this fraction of the
  flux to be aliased.  This parameter is also relevant when you let
  \galsim\ decide how large an image to use for your object.  The
  image is made to be large enough that at most a fraction
  \code{alias\_threshold} of the total flux is allowed to fall of the
  edge of the image.  The default is \code{5.e-3}
```
which was my understanding.  This was something I was going to ping you about later today, actually!  Anyway, the content of the text is a little different, and I'm not sure I understand what's currently here.  Perhaps it's that I find it a little confusing to talk about k modes being aliased when we actually are talking about copies of the real space image.