This whole discussion of Rad Alt involvement is a waste of time. Rad Alt DH's are NEVER used for anything other than a Cat II or III approach UNLESS they are published for a different aproach, and that would NOT be the case in Smolensk. It would be utter madness, perhaps SUICIDE would be a better description, to use it on that approach . I have only seen 2 or 3 airfields in Europe where a rad alt DH is even published for Cat I
Also the 'depth of the ravine' is a waste of time too. It matters not whether it was 100 m deep, 20 m deep or 1000m deep. THEY SHOULD NOT HAVE BEEN THERE.
I still believe it was case of a mistaken visual acquisition - building or road lights or whatever - that caused the increase in rate of descent into the wrong place. As to why they even tried, heaven only knows.