ToME: the Tales of Maj'Eyal

Hello!

Got Premonition from a task.
Then a second task gave me the option to raise this talent +1, and so I did.
But the percentage fell from 12% down to 11% and nothing seems to have improved (even if I am not completely sure about that).
I play a hobbit rouge.

A hobbit rouge, eh? How very pretty...

Anyway, the Premonition spell doesn't scale all that greatly with the talent level. What it mostly scales off is spellpower. Quite likely you had a higher Magic stat or spellpower-boosting equipment early on, and it was reduced by the time you got the second quest.