I was looking into Antumbra (the Rygelon caster dagger) because it seems to sim higher than the optimizer gives it credit for (which is weird.)
The important part is that I found that the wiki implementation is using Spell Hit, and the in-game behavior is one stack per spell cast - which I believe should be Cast Success.
Still not sure why the optimizer likes it less than the sim does. 3df5dc16f2d34ad9b84a53341ec7cc81
BiB: Not Available
BiB locked Antumbra: Not Available
It’s not a huge difference but it seemed to hold true across multiple gear ranges.