Files opening still with Explorer (Explorer Replacement)

When some places try to have me upload a file, it opens in Explorer still.
I have directory Opus set to Replace Explorer for all but the following folders (being the Recycle Bin)
Is there something else that needs to be checked elsewhere?

Also, I know how to change in Explorer but not Directory Opus to have it open Full-Screen?

Jon's explanation, short and sweet:

Thank you, that makes perfect sense. I just thought I was missing something.