Profile.php

<?php
		// Validate that the email isn't used by another staff user
		elseif ($this->web_enabled)
		{
			$rules['email'][] = [
				['Model_Account_User_Site_Staff', 'unique_staff_email']];
		}

Why do you do this? This creates an inconsistency in site staff members. A site staff member's email could reside in two different places: account_users or site_staff_profiles

Right, the email will either exist in the staff members profile if they don't have a user account. If they do have a user account then the email will only be stored in the users details.

This is so the staff member can change their email like they normally would in their account settings without having to change it both there and in their staff profile.