Distinctive ring on destination that is just an extension

I can't seem to get a call directed directly to an extension, rather than a ring group to have a distinctive ring.

If I direct a call to a ring group - I can set the option for a distinctive ring, and that works perfectly, but when I set a destination as a single extension, I cant find anywhere to set this value?

Can anyone tell me what I am missing please?
 
Personally, if I was you, I would stick to pointing the call to the Ring Group and using the field in there to set Distinctive Ring.
Even if there is one single extension, the overhead is tiny and you can use that field easily.

If you really want to send an inbound number direct to an extension, you can use this in the inbound dialplan:

1558487455267.png

Code:
sip_h_Alert-info=<http://127.0.0.1/Bellcore-dr3>
Where (on a Yealink phone):
Bellcore-dr1 = Ring1.wav
Bellcore-dr2 = Ring2.wav
etc...