I think it depends on what your company ops allow. We use MDA for non-prec and Cat I. The DH block is used for CatII and CatIII. We us NO DH for the Cat III, and an alert height of 100"RA, on CatII it depends if RA is authorized or not. If it is authorized we put that figure in the DH and call mins off of the RA or Inner Marker, whichever occurs first. If the RA is not authorized we use the MDA block, and call mins off of Barometric or Inner Marker whichever occurs first.