On HF there is no need for an S-meter standard because it seems to be
the rule to give report 59. If you don't you soon have a bad
reputation of giving wrong reports

A signal doesn't have to be S9 to be heard 5 by 9.
I would usually tell the guy on the other end what
the S meter read, and also how readable he was.
When the band is quiet QRN wise, I could honestly
give a 59 report to someone hardly moving the meter.
OTOH with heavy QRM+QRN someone could be pumping
30db over and still be a rough copy.