No prefix for internal CID

I have an extension with no registered device that is immediately routed to followme for that extension and rings three internal extensions as well as three external mobile phones. I suppose it could conceivably be set up as a ring group instead.

If I call the extension from an external number (that is, I dial our DID with my mobile and at the IVR enter the corresponding extension), the incoming CID name is correctly prefixed with “ABC”.

However, if I make an internal call to that extension, it proceeds to followme, but no CID name prefix appears. Is Asterisk overriding the prefix with whatever extension name is specified in the internal directory or ignoring it? Hard for me to tell looking at the logs, I tried some overrides in the extensions override conf for that extension’s followme, but no cigar.

I’ve never used the Set CallerID Application, thought this might be a solution, but I wasn’t able to figure it out in 15 minutes. Will try tinkering with it later.

Sanity check please; is there some special way of setting a prefix so it applies to internal as well as external calls?