Although the 2nd stimulus had a higher AGI range, that was for the advance payments (stimulus/EIP).
For the Recovery Rebate Credit (essentially missed stimulus payments), claimed on the 2020 tax return, the phase-out is not applied separately to the payment for a dependent. It's applied to the total payment for the taxpayer, spouse if joint, and dependents. So you can't really say that someone is getting a partial amount for a dependent. They are getting a partial amount of the total payment. Look at The Recovery Rebate Credit Worksheet that TurboTax prepares (abbreviated "Recov Rebate Cr" on the forms list).
