Yep, it doesn't work at all without 'directio' as an option at mount time, even just trying to tail from the shell.
However, I was able to get it to work 99.993% of the time (tested with 20,000+ lines) by altering the File::Tail option 'reset_tail' to 1.
That provides the expected behavior, for the moment. There are rare occasions when log lines are duplicated, such as when there are more than 9-10 events per second. However that is rare with my data stream, so this will be good enough for now.