I'm sorry, it's been so long since I've worked on FHFS I forgot what I have and haven't accomplished yet...
I looked at the admin console and it looks like I never actually ended up making it so the admin can control the max file size.
As of 2.0.5 it's set to allow a max of 2GB, or less if the max account size is smaller. But there's no way to explicitly set the main file size.
The entry you see in the admin panel is for setting the maximum ACCOUNT size, aka the maximum space any user's account or all of their files collectively can take up.
I actually have an overhaul of the admin console planned for v2.2 (whenever that occurs).
As of now, the solution for you is to open uploader.js, and replace this line:
max_file_size: '{.if|{.and|{.^maxsizeMB.}|{.<|{.^maxsizeMB.}|2000.}.}|{.^maxsizeMB.}|2000.}mb',
with whatever you want the max file size to be, e.g. something like
max_file_size: '8000mb',
Make sure you include the colon, the comma, the mb, etc exactly as above.... I hope that fixes your problem