When calculating RLSALTs in Oz no notice is taken of CTA base.
We add 260ft (or something like that-can't remember) to every bit of marked terrain assuming that a tower of that height has been built on the hill. Towers higher than that 260ft have to be notified. This figure is rounded up to the nearest 100ft and a 3NM lateral tolerance is included.
We are not allowed to assign a level below the base of CTA - i.e. no control instructions to an aircraft in uncontrolled airspace. It's got nothing to do with staffing - well, not yet anyway.
We will give rlsalt to an acft OCTA on an emergency basis.