I have to say that I find
JP's statement (below) rather odd:
They therefore expected the hill ahead of them to be around 300 ft lower than it turned out to be, and as a result they hit the crest just below the summit.
JP, are you really attempting to suggest that miscalculating (by 300 ft) the height of the hill that they were attempting (in your view) to climb over in IMC led to the crash? Well, I'm sorry, but if that's the sort of thing you used to do in your low-flying past, it's amazing you're still here! I cannot agree that
any Chinook crew, much less an experienced SF crew, would chance their arm in the way you describe (ie attempt to clear a hilltop, IMC, by less than 300 ft) and there is certainly no evidence to suggest that it is what happened (other than what you would probably refer to as
de facto evidence, that they hit the ground)!