As a disclaimer, I was not intending to test this. I set out to try and finish my Research: Yorcia quest. I was feeding TP with my Caduceus (non i-Level club) trying to get those fartknocking snapweeds to stun me, and I noticed this.
First off, Flash Nova's description is "Chance of effect varies with TP." I've long suspected that the real meaning of this is "Additional Effect: Magic Accuracy varies with TP", and posted on the official forums to that effect, but they ignored me. However, it turns out that the description actually just indicates Magic Accuracy of the WS increases in general.
Flash Nova does 925, 461, or 113 damage against Snapweeds
* 100 TP - 113 x15, 461 x2, 925 x1
* 300 TP - 461 x2, 925 x8
So there you have it, "Chance of effect varies with TP." = "Magic accuracy varies with TP."