So yeah, there's a setting in the system config to use x-forwarded-for for user_ip instead of remote_addr (that's explained here - http://manuals.matrix.squizsuite.net/system-configuration/chapters/system-configuration#HTTP-Headers-Settings)
If you can add a link to the above into the user_ip section of the showif page (http://manuals.matrix.squizsuite.net/designs/chapters/show-if-design-area#user-ip) that would probably be somewhat helpful.