I'm a little confused. You need to gain as many Success Levels (SL) as the Power Level (PL) of the spell. You can use excess SL for Embellishments and such.
But when calculating the effect of the spell, what PL do you use? The SL's that exceed the PL or the PL=SL or... the PL+excess SL?
For example, I cast an Eldritch Ball of Flame (PL5) as indicated in GoA p103-104 example.
Eldritch Ball of Flame: PL5 (Willpower x4)+(Success Levels x3) damage.
-I roll mediocre and get SL:5. Just barely casting it. For purposes of damage, do I count the 5 SL to cast it? Or do I subtract PL5 from SL5 and end up with no bonus damage (just Willpower x4)?
-Let's say I roll great and get 9 Success Levels... with PL5, I have 4 extra SL. Do I do (9SLx3) bonus damage or (4SLx3) bonus damage?
Similar question with Duration... I cast a PL5 spell that has Duration (30minutes per SL).
-I roll enough to get SL5 and just barely cast it. Do I automatically get 5SLx30 minutes? Or do I get 0 SL (5-5) and have only a minimal duration of 0 or 30 seconds?
It seems PL/SL get used differently from spell to spell... I confused