A locked HDD with the MS BIOS active will not even recognize an F partition. That is the nature of the BIOS.
Every stock hard drive has an F partition. It's just that it is not formatted by default. And it is negligibly small on an 8GB HDD.
FTP shows the partition size. EvoX shows free space. Since it is not formatted, there is no space available. Formatting it should make both your FTP client and EvoX display the same value.