detail log permissions warning

I'm getting this error in the logs when a COA packet is being
processed by the coa-relay server:

File /var/log/radius/radacct/detail_coa permissions are 0640
(rw-r-----) not 0660 (rw-rw----))

The configuration for that detail log is:

detail detail_coa {
  permissions = 0660
  group = ${security.group}
  filename = ${radacctdir}/detail_coa
  escape_filenames = no
  header = "%t"
  locking = yes
}

Is that permission setting possibly being affected by the system umask ?
It seems to work, but throws that error regardless.
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