Configuration issue with siproxyd

[XSRD]

Hello,
I am encountering an issue with siproxyd

My setup is the following
Site A pfsense 2.6
LAN 192.168.0.xx/24
WAN 10.0.1.xx/24 (subnet with isp router and pabx and the site A phones)

Site B pfsense 2.6
192.168.11.xx/24

I have a IPSEC VPN with 2 phases 2 to channel traffic between each site
192.168.0.xxx <> 192.168.11.xxx
10.0.1.xxx <> 192.168.11.xxx

Base communication is fine, i can ping everything, access server from all sides, including the PABX wich is on the WAN side with ip 10.0.1.49 from lan from both sites

My problem is that i have phones on sites B that cannot register correctly
i'm seeing the sip paquets on my wan interface not being nated and just routed, except for one ip from side B wich is nated to the wan address
I cannot seem to be able to make siproxyd to work as my choice of interfaces does not include the ipsec interface enc0
i've tried to add it manually to the conf file and reload the pfsense, but it didn't seem to have any effect.

i do not have any control over the pabx (or i wouldnt have set up the things like this)
so i have to make it works.

Strangely, i had the possibiltiy to make it work before with site A pfsense and a Zeroshell on site B and with an openvpn tunnel,
i had issues but they were solved by a good old reboot.

My question being,
is there a way to use siproxyd with an IPSEC vpn ?
if so, what am i missing
if not possible, should i go back to the Openvpn tunnel as it seemed to be a functionning solution ?
or is it a better approach to that issue ?

Thanks in advance,