Miscasting protection & spell school levels

[widrox]

I have a question concerning the miscasts. Does each level in the magic school of the current spell is what matters the most, or is that the sum of all most important in the possible percent of miscasting the spell?

E.g. let us take the Mephitic Cloud as an example:
1. Conjuration 1L Poison 1L Air 2L
2. Conjuration 0L Poison 0L Air 4L

I.e. does the spell "Mephitic Cloud" has the same possibility of miscasting in both examples or one of the gives more protection from it?

[Galefury]

Only the sum is relevant. Spellcasting skill and int too of course.

[danr]

The other consideration that's relevant is that option 1 takes less XP invested in skill levels. But if it's your only poison spell then it would be a waste to train poison magic just for that.