In that case, you can start FOP2 in debug mode and capture events to see if you have Peer registration events in PJSIP. Maybe there are no such events, or maybe they are different to the chan_sip ones and FOP2 needs to be updated to support them... if you can make a test try this:
service fop2 stop
cd /usr/local/fop2
script capture.log
./fop2_server -X 1
At this point FOP2 will start and you will see output with AMI events on the console. Then log to FOP2 with your browser and check sip status. Then fire up some soft phone and register to Asterisk, then unregister (that should fire some AMI events about the SIP device status). Then stop capturing and resume normal FOP2 by issuing these commands:
ctrl-C
exit
service fop2_start
You will then end up with a capture.log file that I can inspect for such registration events. You can send that file via email to nicolas at house dot com dot ar or post it here (although it might contain some information that you might want to not publish in a public forum).
Best regards,