firewall logging - log all incoming traffic?

Is it possible (using standard Apple firewall application) to get it to log all activity, including incoming. At the moment the log is showing the occasional blocked item. I'd like to see everything.

At one point I was able to see all incoming activity - until I went to Preferences to check what the settings were and after exiting I discovered the log was not working in the same way.

Can anyone explain this?

I know using the command tail -f /var/log/appfirewall.log in the Terminal produces a 'live' log. Its contents have also altered and no longer show any incoming traffic.