UNC vs absolute performance when target is the local device

  absolute-path, file-io, unc, windows

We have desktop application that uses filesystem files for its processing,
The app is using UNC ("MyShare") path on the code (e.g: File.Copy() operations),
We saw for some customers, when using UNC path we receive errors e.g:

System.UnauthorizedAccessException: Access to the path is denied

Once we changed the path to be Absolute path (D:MyShare), no exception were thrown.

This leads to following assumptions when using UNC:

  1. The system probably query DNS/Netbios for resolving hostname to IP (overload but should not cause issues)
  2. The system might "trigger" additional OS security layers, e.g: permission for the share or local Antivirus that might sniff and check network adapters traffic
  3. The system might trigger external firewalls sniffers

Are my assumptions correct?
I am trying to understand thee overhead of using UNC over Absolute when not required

Source: Windows Questions