Been a while oops. But yes This is exactly what I meant. What had happened with that windows backup was I had my backups share set to use the Cache drive just like my normal day to day storage shares but the backup I was running was much larger than my cache ssd. I remembered this would cause an issue for the backup about halfway through the ssd filling up so I turned on the mover and then it managed to limp along until I had written close to 2 TB into that folder. (It was an unnecessarily overly comprehensive backup which included my entire downloaded steam library which has no need to backup.) once I realized the faults in that method I set a minimum free space of like 100gb for that share and disabled caching because the cache disk is what had caused those backups to fail in the past not the actual filling of the 2T disk. It has since leveled out more across my drives. (granted I have still eaten up over 4TB and will need to buy more drives soon but alas.
Anyway, Thanks for the help and information!