The logo URL field in Branding / Login page tab is not usable: the field require a nuxeo URL that you might not know.
Things to do:
- Use the same Logo Image / Width / Height / Alt fields than in Main Pages tab
- Move these fields to Login Box section
- If these fields are already set in Main Pages, it might be useful to reapply the same values and let user update them if the values are not relevant.