I will tell you this, I skied much more sketchy conditions on the lower half of Castlerock yesterday then I did on those 2 runs. Castlerock had dirt, rocks showing, fast grass. You name it. There is no real reasoning on trail openings in my opinion. They are random as best as I can tell.
Well at least Castlerock has a hike required which would in theory weed out many people from attempting it and restricts it more to the real "hardcore" skiers that can handle it.