Folder permissions for uploads, images and snapshots

Hello support, i'm looking for some wisdom and guidance if possible.

I have recently change my "uploads" directory outside of my WordPress installation.

Old structure:

(public folder is where WordPress is installed)

New structure:

Sub-domain points directly to the images folder

Everything uploaded to the site is now saved in the new images directory. The reason for doing this, is because I now use a sub-domain to serve my images.

The problem I'm having is with image uploads and with Snapshot, where the new image and snapshot directories need to have folder permissions set to 777, where the old structure happily ran at 755.

I have made sure the correct user has owner ship, and tested setting different parent-folders to 755, but when I upload images, or run snapshot, I constantly get errors, stating the directory is now writeable, or images can not be move and I'm forced to use 777.

Everything works great when using 777, however I'm very concerned with using these permissions.
I'm looking for any support you might be able to provide, that will allow WordPress images to be on a sub-domain, and when uploaded automatically use the sub-domain, but with stricter folder permissions.

This is a VPS Server so I have full access if any specific changes are needed.

I appreciate any help or support you may be able to provide.

Thanks again.