Issue with a fax on a 2 leg call.

[Pbxpoweruser]

We are having an issue with the redirect of a fax line. We have a fax number coming in via SIP trunking where we use G729 as a codec which we terminate on a Phantom TN (With CLS MPTA and DTN) and we DCFW back out to our fax server (We tried sending it back ou SIP and PRI which made no difference). Our SIP provider does not support T.38 so we must force G711 however we are never able to get it to negotiate at G711, it always defaults at G729.(The first leg of the call needs to terminate on the PBX before the call forward occurs which I believe is where the issue lies)

All other physical fax machines are working fine and negotiate to G711 automatically. We have tried a few things however we are not sure

Any ideas?