I generally recommend against using 0664 unless you are a Linux geek setting up your own server and know very well what you're doing. In all other cases 0664 is dangerous. It's best to make sure that all of your files are owned by the FTP user and have 0644 permissions.
Further reading to understand how all of that works (sorry, in English only):
- www.dionysopoulos.me/blog/72-777-the-number-of-the-beast.html
- https://www.akeebabackup.com/documentation/akeeba-backup-documentation/how-your-web-server-works.html
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!