The negotiations between Councilmember Rosenthal and TF Cornerstone hinged on two thresholds of affordability. With regard to the first, "Rosenthal told TF Cornerstone that the threshold to qualify for the least-expensive units—the ones that would be set-aside for some of the poorest New Yorkers—should be raised." So "[she] increased the eligibility cut-off from 40 percent of area median income, or A.M.I., to 60 percent."
Then comes the second question of affordability —namely, what it takes for middle-class, or upper middle-class, families to live in extremely expensive neighborhoods like the Upper West Side. The increased level of the lowest threshold of affordability, "allowed [Rosenthal] to negotiate more 'affordable' units for much-higher-income families. Rosenthal told the developer to dedicate 10,000 square feet, or about 20 more units, for moderate-income households…Those new units will be dedicated to households making between 175 percent and 230 percent of the A.M.I."
Hutchins goes into a lot more detail about the political blowback and other implications of the deal between Rosenthal and the developer.