Whats up with Stoneskin?

[Coglin]

Spells not effected by attributes like siphon TP will follow the 20%/10% penalty as long as you meet the minimum rank requirement. All of this is regardless of whether you are playing as a discipline of war or magic. .

Not to get of topic, but for the sake of accuracy, siphon TP is effected by a stat. Piety modifies the amount of TP, Magic points, and hit points(drain) taken from the target, with siphon TP, siphon MP, and drain, respectiely.