How difficult is it for PM to sing out the required ht against DME range and for the PF to adjust accordingly
The PF should already have the chart in front of him and he should be referring to it. The support call by the PNF is a back-up to what the PF should already know. To rely on just one pilot calling the chart details is poor airmanship as PNF's have been known to call erroneous heights versus DME distances. The PIA A310 crash at Kathmandu, the Air Manila (?) 707 crash 20 miles from Manila and many other similar CFIT accidents attest to that.