Request-line тоже меняется см ниже (во вложении скрин настройки), я напомню я не использую динамическую регистрация, идентификация происходит по From:
74956207068@192.168.31.8Session Initiation Protocol (INVITE)
Request-Line: INVITE sip:302@192.168.31.8 SIP/2.0
Message Header
Via: SIP/2.0/UDP 192.168.31.8;rport;branch=z9hG4bK3vp4BKg9gHcUS
Max-Forwards: 70
From: "102" <sip:74956207068@192.168.31.8>;tag=ZHSN1tXUXZeyF
To: <sip:302@192.168.31.8>
Call-ID: 5049dce8-6d02-1234-aea3-a8f94b03a44e
CSeq: 79844 INVITE
Contact: <sip:74956207068@192.168.31.8:5060>
User-Agent: TAU-8.IP-W/2.0.0 SN/VI09000229 sofia-sip/1.12.10
Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, PRACK, MESSAGE, SUBSCRIBE, NOTIFY, REFER, UPDATE, INFO
Supported: timer, 100rel, replaces
Session-Expires: 1800
Min-SE: 120
Content-Type: application/sdp
Content-Disposition: session
Content-Length: 256
Message Body
Session Description Protocol