I might have underestimated the size as I was doing it from memory. Callistemon sieberi has leaves that are 2-5cm long according to Plantnet so maybe the moth was 2.5 cm long, but it was quite small and about twice the size of one I saw last week.
Given the uncertanty re size I'm not sure we should identify a new species for CNM simply on presumed size alone without other supporting evidence. Could easily be Acyphas (genus) in my opinion, but again distinguishing species can be difficult without supporting information.
So with wings out it would have a wingspan of about 4 cms. Wingspan of Acyphas chionitis female is listed as 3.5 cms, so I think it is within variations due to genetics and nutrition of an Acyphas.