There appear to be differing thoughts both side of the pond. I considered for simplification Decision Altitude DA to be used only for Cat I ILS using baralt. Decision Height is used for Cat II and III ILS using radalt.
FAA TERPS: DH Decision Height. The height, specified in mean sea level (MSL), above the highest runway elevation in the touchdown zone at which a missed approach must be initiated if the required visual reference has not been established. This term is used only in procedures where an electronic glide slope provides the reference for descent, as in an instrument landing system (ILS) or precision approach radar (PAR).
FAA TERPS: Radio Altimeter Height (RA). An indication of the vertical distance between a point on the nominal glidepath at DA and the terrain directly beneath this point.
Decision Altitude normally 200 ft though may rise due to increase of glideslope angle for obstacle separation. If you wish to include DH with DA then add THR elevation? Decision Height depends on type of ops, ac performance etc.
There seems to be no MDH defined for onshore FAA ...... even though we might use it for offshore ARA being a non-precision approach using radalt?