It is my guess that FARR takes the file size content of any file from the Windows file system. So you might have to think differently about the solution to your problem. According to my Google-fu, there are many requests for showing the exact file size in Windows Explorer, but not much answers.
Microsoft tells us that there is no way
to change this.
A bit of digging revealed: SizeInBytes
which is a tool that makes Explorer show the exact file size. While this software is free, it does require you to have a license for it's parent software SmartFTP...which is costly at 79.95 USD (the cheapest edition).
This is a long shot, but you could get a copy of Directory Opus, configure it so that it takes over the function of Windows Explorer and make files show their exact byte size that way. It is also not cheap at 85 AUD (Australian Dollar). There is a lite version of Directory Opus at half that price, but I didn't look if that version can replace Windows Explorer or not.
You might have guessed it, this has been a pet peeve of mine for as long as I use Windows. Microsoft calls this lack of configurability 'simplicity', while I think it should have been a Windows setting from the get-go. In Windows XP you still had an option to show everything in KB, but that has been removed since Windows Vista, which rounds up and down in very weird ways sometimes. Almost all 3rd party file managers show you the file size the way you want it to, but that won't help you with FARR.