Pretty consistently across the board, any area spell that has a save for 1/2 will have this affect:
Damage starts at 100.
1st critter doesn't save -> 100
2nd critter does save -> 50
3rd critter doesn't save -> 50
4th critter does save -> 25
5th critter does save -> 12
6th critter does save -> 6
This is the reason that chain lightning is by far the best area spell. It sets a new amount of damage for every target, and then checks that target for the save. At least Gordon fixed the fact that chain did level d6 to the first target, then level d8 to the next targets. Setting a limit on it wasn't a bad idea either, although how many times will you use it with more than 8 targets?
Now if we want chain to continue to be the pantheon's gift to players, we can certainly leave this. Although it renders pretty much everything else impotent in comparison (I watched Talesian ultra blast 5 mobs, and by the 5th mob the ultra blast did 4 points of damage).
It's an easy fix, all we have to do is make sure we catch all the area spells that we don't want this to happen to. I'd imagine this would be most of them.
Let me know what you think, this would increase player power probably, but it would balance out the spells and their effects.