SP21/Pontoon indices for doubling A,7-A,9?

[lij45o6]

Because a level 3 count provides more advantage in SP21/Pontoon than it does in traditional BJ by a good margin. If you add a bunch of indices on top of it, each count increment can give you a sizeable advantage. The game swings like a mofo because of its high variance, but there's good money to be made nonetheless.

Curious as to why a L3 point count "provides more advantage" in Sp21? What analysis have you done to suggest that going above L2 is better? Is it better for betting or playing? Both?

What warrants playing over L2?