you make scripts like this, but we don’t use it at this tutorial

To edit spells: Go into game mechanics and then into spells. Choose the spell class and click on the spell.

<Base> = starting strength
<PerPower> = extra strenght per spellpower

My modified cotn:

<Item>
  <Base>16</Base>
  <PerPower>4</PerPower>
</Item>
<Item>
  <Base>20</Base>
  <PerPower>5</PerPower>
</Item>
<Item>
  <Base>40</Base>
  <PerPower>8</PerPower>
</Item>
<Item>
  <Base>80</Base>
  <PerPower>10</PerPower>
</Item>

If it doesn’t looks likes this, it’s probably because you had taken a effect. Only take the name on the spell, not with effect