Can't disable site admin override

I have installed multisite privacy on my network and checked the following option (and default setting): 'Only allow logged in users to see all sites.'

I have selected 'no' to 'allow override' and have 'updated all sites with the default privacy setting'.

However, under 'settings' / 'reading', individual site admins are still given the option to decide whether or not 'visitors must have a login' to be able to access their site. I only want the network super admin to have the power to dictate privacy levels for individual user sites. Is this a bug or have I configured this plugin incorrectly?