Divine Intervention - no additional chance for cleric AA?

[BWStripes]

I spent about 3 hours looking at this on request of a friend, so l will feel pretty stupid if it is here, but I can't find cleric Unfailing Divinity AA or character CHA being added to the DI save itself.

I can only see Unfailing Divinity adding a 30% chance to trigger a 1500pt heal.

I'd written up some code to factor in CHA, the cleric AA, correct the 50k heal to 8k for the DI save and also update the additional chance with UD ranks 2 and 3, but before I continue, someone please correct me if I'm completely wrong!