Be aware that <Files> also means "only files". That is, the string inside <Files> is compared only to a filename, not to a file-path. Therefore, you use the start anchor in <Files> but not in RewriteRule. <Files> ignores directory-path info, while RewriteRule does not, since it works with URLs.
I decided to go the mod_rewrite method because I have other rules that rewrite [domain.com...] >> [domain.com...]
That in conjunction with errordocument was resulting in rewriting the path to my errordocument to the address bar. Since I'm using error.php?404 or error.php?403 etc I thought it best just to force 403 so that the inner-workings of my errordocuments stays hidden in the event that someone asks for [domain.com...]