How is reserve reroute pay (into an X day) calculated?

For example, assume:

• A 4 day trip that is scheduled to end at 2000 with a deadhead on day 4 back to base.
• Due to a delay on the second to last day, the last fight back to base departed before the reserve's second to last leg arrived. They ended up going to a hotel.
• The reserve was extended into an X day to return to base and was released at 0900 on day 5 via a 2:00 deadhead.

Is there reroute pay above guarantee and if so how is it calculated? (section 23.L.9 was confusing to me)

Is a payback day added to the reserve's schedule much like a GS payback day?

Thanks!