Okay, apparently my earlier theories aren't quite right. The threshold for fearing something is apparently variable. I've successfully feared creatures with as low as a 132, but I've now had rolls as high as 135 and 136 make them flee and get RT. I also killed one just now with a 141 endroll, so maybe the instakill chance has the same thresholds as the fear?
You gesture at a Grimswarm troll cleric.
CS: +507 - TD: +402 + CvA: +11 + d100: +19 == +135
Warding failed!
The troll cleric blinks for a moment, then runs northeast!
Cast Roundtime 3 Seconds
You gesture at a Grimswarm troll guard.
CS: +507 - TD: +401 + CvA: +8 + d100: +22 == +136
Warding failed!
The troll guard struggles to maintain composure.
Cast Roundtime 3 Seconds.
You gesture at a Grimswarm troll soldier.
CS: +507 - TD: +380 + CvA: -13 + d100: +27 == +141
Warding failed!
In a panic, the troll soldier discards her gear to aid her flight!
The troll soldier blinks for a moment, then runs off!
[You have earned 65 prestige points.]
Cast Roundtime 3 Seconds.