Hi Ed,
I've only done ribs 3 times, once rolled and twice with the Charbroil rib racks someone recommended (I think it was Stogie).
With the racks I cut the ribs in half and didn't experience any dryness at all on the ends.
However, I always wondered how people do whole racks without rolling them. It would seem that the ends of the racks would be outside the diameter of the water pan and subject to much higher heat...