Leadership and leveling

[Hazimel]

There is something unclear for me.

I thought that if your attack is higher that enemy's defense , your damage is 300% but you tell me it is 10 % more damage for each attack point.
I thought that your the spell inflict 10 % more damage very 7 points of intelligence, not every single point.
At least, this is written in the official rules (but they may be wrong)

So I am confused.
Could someone explain what is the true calculation ?