On subject of drop-in files for systemd unit files.
Qubes has:
/lib/systemd/system/tmp.mount.d/30_qubes.conf
[Mount]
# Default initial size is '50%' (of physical RAM at system startup)
# Because of memory ballooning this happen to be very low number
Options=mode=1777,strictatime,size=1G
Dunno if that works though.
mount | grep -i strictatime
No output.