Copy Windows 10 media to local folder for "Turn Window Features on or off" to find

As with all previous editions of Windows, I've copied the sources folder from the ISO to a local "C:\Media\sources" folder. I've also set the SourcePath in the registry in a couple places in HKLM. However, when I try to turn on windows features, the wizard wants to go out to Windows Update to download the features, instead of relying on the sources folder. That's also not working, because of the dreaded 0x800F081F error. I can check for windows updates, and it says there are no more updates available, so I know I'm connecting, but it fails during Feature on/off.

Has the Windows 10 method of setting a media source folder changed? What is the correct method? I need to enable HyperV, WPAS, IIS, and other developer features.

Edit: Forgot to say ... after configuration with SourcePath, it's either not attempting to use the local copy, or it's not finding it, possibly needing additional registry entries.