Multisite logout redirect

Hi, I wonder if anyone has run into this problem before but I cannot find an answer.

I have multisite set up. All works fine. The only problem is when logging out of a sub folder site and the behavior is the same when I domain map and when I dont. It will look for this for example and wont find it.

https://site.com/subfolder/wp-login.php?action=logout&_wpnonce=cbea2555c4

Having read a bit around I thought the default logout behavior always sent the user to the main logout page.

https://site.com/wp-login.php?action=logout&_wpnonce=cbea2555c4

The same happens when I login with meta widget.
I get the login page like this
https://site.com/wp-login.php

then it sends me to
https://site.com/subfolder/wp-login.php?redirect_to=http%3A%2F%site.com%2Fsubfolder%2Fwp-admin%2F&reauth=1

I am on a windows server and have looked at using a redirect in the web.config but am able to redirect the opposite way, ie, from
https://site.com/wp-login.php?action=logout&_wpnonce=cbea2555c4
to
https://site.com/subfolder/wp-login.php?action=logout&_wpnonce=cbea2555c4
but not the other way around.

Any pointers would be great.
Thanks in advance

Richard