Incapsula is deployed as a reverse proxy in front of your WordPress application. This means that all traffic coming to your site through Incapsula will be seen as coming from one of Incapsula IPs.
In order to make sure that your WordPress and existing plugins get the correct user IP we have created this Incapsula plugin.
The Incapsula plugin will make sure that any reference to the user IP in your WordPress will use the correct IP address.
You can also find the plugin here: http://wordpress.org/extend/plugins/incapsula/