In reply to iamaclimber:
Having completed the WML last winter, I fully agree with the other responses to your OP; I wouldn't consider myself ready for assessment until I was able to navigate competently in near zero viz on unfamiliar terrain - which happened to be the senario we were faced with on our exped! Basically, do as much night nav. as possible, in a wide range of conditions, in unfamiliar and pretty featureless areas.
As has already been said, you could end up anywhere where the conditions are suitable at the time. For the record, my training week included Creag Meagaidh, Aonach Mor and Buachaille Etive Mor. For the assessment; Coire Nan Lochan, Beinn Dorain and Beinn Inverveigh.
Good luck.