Consider the scenario with a WebDAV mapped drive on a Windows client. The drive's capacity is reported different than the actual capacity of the disk on the file server.
Research on WebDAV protocol RFCs and verification from Microsoft's product team confirmed WebDAV protocol doesn’t support querying server’s disk capacity. With this constrain of WebDAV protocol, Windows client sets WebDAV mapping drive’s capacity the same as its System Drive.
This is by design. A WebDAV mapped drive's capacity is set to match the client machine's System drive capacity. This means that the capacity you get from a WebDAV mapped drive is the same as your local System drive. System drive is where Windows is installed.