I have only made it to the end of the campaign once, so I don't have a really good point of reference, but I thought the Wraiths were unusually passive too. Quite often I would spot them at a distance, withdraw, gather up my guys to engage and end the turn. When I would scout forward again the Wraith would usually be in the same spot (not having taken cover or moved or anything).
I was running without the CE Balance mod turned on though.