Ring tone

[nicolinux]

Hello, i have a few T20P yealink phone and a Yeastar Mypbx. I have configured the contact in each phone, putting all the extensions in a group named "work".
After that i have given to the this group a different ring tone, ring6.
When an extension calls another extension the phone use the proper tone (ring6) and when there is an external inbound call the phone is using the default tone, ring2.
The problem arise when userA answer to an external phone call and wanto to tranfer it to userB. UserB's phone is ringing using the default tone (ring2) and not the group tone (ring6).
In a few word, the customer woud like do know if the incoming call is an internal call or is an external call been transferred
can you help me ?
Nico