@Reiker: Those mobs had Call of the Zero. That was their anti-exploit.
The 2% or 100 damage is the right answer. I remember most FG's summoning, same for the IG's after the Diplomat, This hypothesis is supported by the spawn log based on levels.
- Fire Giants ranged from 47-51 in level, a 5 level spread.
- Fear mobs ranged from 48-52 in level, a 5 level spread.
- Hate mobs Ranged from 48-52 in level, a 5 level spread.
Now, it would be easy based on these facts to say that mobs 49+ would be your summoning threshold. This would leave
some FG's to Summon,
some IG's to summon and
most planar mobs to summon.
This would also fit the sketchy recollection I have from Kunark of Dar's/Kor's/Jin's not using summon, but the frog after Dar's (Bok's)
could, but not always. 57+ is the enrage barrier.
So, based on the above info. I have to put my support to > 48 being the summoning threshold.