NTFS Disable 8dot3name

I wonder if the reported MFT size is fixed from the start, in the format faze, or varies with each file added or deleted?
Is it preallocated for the entire drive, like X bytes for Y bytes of data? Or X bytes per each data cluster?

I can see different MFT/Data in members posts:
https://forum.storj.io/t/disk-usage-discrepancy/24715/467?u=snorkel

https://forum.storj.io/t/disk-usage-discrepancy/24715/262?u=snorkel

https://forum.storj.io/t/the-hard-drive-is-full-because-storj-probably-hasnt-deleted-anything-anymore/25510/6?u=snorkel

https://forum.storj.io/t/errore-disk-space-used/8798/6?u=snorkel

So it’s dinamicaly allocated.