I read your question not as to where to enter your value... You only fill out the DH-field during a lovis-approach, as already stated, and use the MDA-field for everything up-to-and-including-CAT1.
But if given 2 different values, a DH and a RA, I would fill in the RA-number in the FMGC, because the a/c will generate an autocallout at minimum, based on your radio-altimeter, not your baro-altimeter.
Hope it helps!
[ 20 February 2002: Message edited by: Pegasus77 ]</p>