Wizard's Communion and Penetration

[Richard_Love]

@RainOfSteel

ArM5 p.82:

Penetration Total: Casting Total + Penetration Bonus - Spell Level

...

ArM5 p.160:

"However, the target number for the spellcasting roll is the spell's level divided by five." (The "spell's level" being the target spell for Wizard's Communion, not the level of Wizard's Communion.)

...

In ArM5, five magi get together to use Wizard's Communion on an Aegis of the Hearth level 50 (one of magi personally knows that spell) who each know Wizard's Communion at level 20, for a total of 100, double the level of the Aegis of the Hearth. The target number to cast the Aegis of the Hearth is 10. The primary caster has Rego 25, Vim 25, Artes Liberales 5, Philosophiae 5, Aura 5, and rolls 5 for a casting total of 70, easily beating the target number of 10. The primary caster's Penetration is 2.

70 + 2 - 50 = 22 Penetration Total

It could be written clearer, I suppose, but the "Spell Level" used for the Penetration calculation is the reduced "Spell Level" provided by the Wizard's Communion. The Penetration is meant to be how much the Casting Total exceeds the target Spell Level (+ bonuses). Wizard's Communion reduces the target Spell Level for casting so increases the Penetration. So, the Penetration Total is:
70 + 2 - 10 = 62.

@RainOfSteel

I went back to ArM4 on p.158, and it is even more specific:

The rules are different in ArM4 for lots of things. Especially Penetration.