Hi @Jeff_Thorpe, Thanks for the response.
This is indeed a stand alone PowerApp with SP List as a back end.
Unfortunately, creating a PowerApps custom form in the Sharepoint Library would necessitate developing another "app" then supporting two versions of the same. I can't go there with this particular project. \
Hm. Bummer. Would be nice to have the ability to control access to the "back end" of the app. I think whats missing is the concept of an APP ID between stand alone PowerApps and Sharepoint lists.
Ideally, I would control USER access to the PowerApp via AD Security Groups, then control APP access to the Sharepoint list with an App ID. Then only the APP has read/write/delete/etc. permissions on the list, not individual USERS.