Jayteeto think you hit the nail on the head!
DA if QNH and the equivalent DH (in brackets on the plate) if you fly QFE.
Most UK IFR Operations use QNH.
The procedure for setting bugs is necessarily type specific and in my view, as an optimum, should provide a clear visual indication to the crew(s) that the minima is achieved AND an aural warning that the minima has been breached AND the margin between both the indication and the warning should be sufficient to prevent the aural warning interfering with the MCC calls at the applicable minima. We have this capability on the latest 225 software but for other types the bug setting procedures may involve compromise against the optimum.
In the 225 we use the DH value (in brackets on the plate) as the reference from which we set the aural warning some margin below that value.