Right now I've set owner to the directory to www-data. So as long as it's the same as the service, then 755 is sufficient? For non-public directories, can those be less than 755?
Here's the commands run to get a sense of the current config, however I still don't see some operations made within xenforo (i.e. style upload) on the site able to write properly. As a test, recursively set the whole xenforo directory as 777 and it seems like xenforo isn't able to write properly to some directories interestingly.
Bash:
chown www-data:www-data /my/web/directory -R
find /my/web/directory/ -type d -exec chmod755{}\;find /my/web/directory/ -type f -exec chmod644{}\;