Indiana pays UM and UIM as the difference between your limit and what the other party paid
Indiana's rules are in IC 27-7-5-2 (offer and rejection), 27-7-5-4 (definitions) and 27-7-5-5 (limits and the maximum payable). The minimum limits are in 9-25-4-5, and the injury deadline in 34-11-2-4.
Read how stacked and single-policy coverage differ in Indiana, check what section 27-7-5-5 says, or see how UM and UIM work in Indiana.