Use with NodeReference - how to add to pattern, just title of node being referenced

Syntax issues in pattern.

Have two custom fields set up in a custom content type (for clarity's sake, field "field_A" and "field_B". One of these (field_B) is a node reference. I wish my automatic nodetitle to be "A - [title of field_B]".

The token for a node reference title is [title]. I've tried (amongst many others):

[node:field_A] - [title:field_B]

...but that isn't working. I'm unfamiliar with the syntax here, should hopefully just be a quick pointer from someone experienced? I want to use the title from the node referenced in "field_B".

As a sidenote, the above works in the sense that it populates the call for [node:field_A] with the custom field input, but it's not hidden? I have the "Automatically generate the title and hide the title field" option enabled.

Any help much appreciated!