Yes the terrain and weather are very important. When I think of hill running I always think of Ron Hill leading the Three Peaks, then getting lost in the mist and ending up about 5th. He also led the Ben Nevis but fell on the descent, came home covered in blood, way down the field: and on the road and track Ron was a world record holder, a European and Commonwealth champion, but he never won the Three Peaks or the Ben Nevis (if memory serves).