Remote 57i

Hi I have one remote 57i
I guess I have a few questions…
The asterisk server is set up at a remote site it has a whole ip address forwarded to it with pass through set on the router…
The remote 57i is behind a xyzel 661 router with VOIP Qos set.

In Global SIP settings I have set the

Proxy Server
Outbound Proxy Server
Registrar Server

all as the Remote asterisk server external IP,
I now see this is wrong…

Given we have one phone there what should I have set in those settings ?
Shortly there will be one or two other phones on site…
What if anything needs to be changed to allow more than one device (Extension) to be used at the remote site…

currently the phone is constantly de registering…

half an hour ago it looked like this…

711/711 .***.***. D N A 10312 Unmonitored

now it looks like this…

711/711 (Unspecified) D N A 0 Unmonitored

I have another 57i which is local to my asterisk server, however one of the extensions on it is a remote extension to another asterisk server, this phone works perfectly… No problem… No port forwarding etc
all the
Proxy Server
Outbound Proxy Server
Registrar Server
IP’s are set up as the remote Piaf server never had an issue…
Is this set up correctly ?
It always seemed to work fine …