Methodology for HUD Income Levels?

Hi,

I am trying to replicate the HUD AMI Household income distribution using the 2017-2021 ACS PUMS data for Colorado (see https://www.huduser.gov/portal/datasets/cp.html) .  Does anyone have a source for the algorithm used by the Census Bureua to calculate the counts HUD uses?

Specifically, I'd like information estimating the number of households at  30% AMI used by HUD CHAS data

This working paper presents analysis of custom tabulations of the 2006-2010 American Community Survey (ACS), known as the "CHAS data." The CHAS data combine ACS microdata with HUD adjusted median family incomes (HAMFI) to create estimates of the number of households that would qualify for HUD assistance. Using these data, I estimate the number of rental units and ownership units that would be available to prototypical households at specified income levels.

https://www.huduser.gov/portal/publications/workpapr.html?search=program%20evaluation%20division

TIA

AB