Well, not just the “reference” is different, the source is different as well. DA/MDA = barometric altitude, DH/MDH = radio altitude. DH therefore is never reference to airport elevation.
I found a picture of the Airbus FMS, it states BARO and RADIO, which is correct. Some aircraft referred to it as MDA and DH. Its a bit weird to use the term MDA in the world of CDFA approaches.