Let's say you have a magic system similar to Lenga in your Action! System game. Three new attributes, spells are skill rolls based on one of the three attributes.
Roll nine dice and arrange them in a 3 X 3 square. You have eight chances to roll a syccess, how you determine those changes depends on the attribute related to the spell. Consider the dice positions below:
1 2 3
4 5 6
7 8 9
If the power attribute was the base of the spell, your eight chances would be determined by eight lines. Namely: 123, 456, 789, 147, 258, 369, 159, 357.
If the aptitude attribute is the base of the spell, your eight chances would be determined by corners. Namely: 412, 236, 698, 874, 426, 842, 684, 268.
If the defense attribute is key, total all four dice and divide by three. Yes, this gives defensive spells a slight advantage, but it's not as much as you would think.
For example, casting a spell that turns a pound of lead into a pound of gold has a TN of 30. It relies on the 'aptitude' attribute which for you is 6. Your skill with this spell is an 8. Rolling attribute (6) + skill (8) + 3d6 versus 30. This means you need to roll a 16 or better. Instead of the 3d6, consider the following:
You roll nine dice in this pattern
3 4 2
5 1 6
2 6 5
Because it is an aptitude based spell, your eight 'corners' yield:
You have three successes. This means you get two extra dice for effect.
Give it a shot.