Denver Property Tax Relief phase out

We are unable to find the specific phase-out percentage needed to calculate rebate amounts for eligible households. The current implementation (PR #4833) defaults to assigning maximum rebate values

Review PR #4833 and the attached example first, then trace where Denver Property Tax Relief rebate amounts are assigned. Confirm the authoritative phase-out percentage for eligible households and update the implementation so amounts no longer default to the maximum rebate values. Done means the phase-out is applied correctly and the relevant behavior is verified.

Written by the indexing model from the issue text.