Incoming call from SIP Proxy to Asterisk

Hi,

I have asterisk register two users (client-1, client-2) with a SIP proxy. I have the same two SIP client registered with asterisk. Now my dial plan setup is such that any call from client-1/client-2 is forwarded to the SIP proxy and the SIP proxy then takes the routing decision. Calls coming from SIP proxy will dial out the respective user. Asterisk is required to stay in the signaling as well as the media path.

Client-1--------> Asterisk-----------> SIP Proxy
Client-2<-------- <-----------

So for call from client-1 to client-2, asterisk forwards the INVITE to the SIP proxy but when the SIP proxy gives the INVITE back to asterisk (as asterisk registered client-2 with the SIP proxy), asterisk is challenging the incoming INVITE. It seems asterisk is seeing the INVITE from SIP proxy as INVITE coming from client (this is I guess as per the lookup that asterisk performs). Is there a way to have it first match the INVITE host IP rather than FROM user first? Or rather is there a way to have this setup working?

Regards,
Maytan