clarification about session in internal script logging

I am using clicky.log() as well internal script logging from server side so that I can attach session data at later time after user logs in as it is a single page application. I am using userid as custom data from internal script and sending other parameters as well except session_id parameter. The problem is, even if two users are using the website on same local network on different computers, the visitor log for both the users are getting merged as single user. I think this happens because I am not passing session_id. What I should ideally send as session_id so that logs with clicky.log() and internal script is consistent?