I don't have a technical answer to give you, but if the recommendation
is to work at around -23 dBFS RMS, I would agree that this is
sensible.
If you establish your "0 dB" point at -23 dBFS, you have an amount of
(digital) headroom that's approximately what you would expect in a
traditional (analog) mixing desk -- more than 20 dB above your "0 dB"
point before you completely run out of voltage rail.