roth IRA conversion

Using Turbtax Premier 2022, doing what-if planning for a Roth IRA Conversion. I am retired and have a very simple return, no special income or deductions. Let's say my income for 2021 is $2K. When I enter data for a $30K Roth conversion, the Total Income field shows $32K as expected. However, when I enter $35K conversion, the Total Income is $40K instead of the $37K I had expected. Similarly, a $40K conversion produces a $48K Total Income.  Does that seem correct? Shouldn't the Total Income be $32K, $37K, and $42K, respectively? 

Thank you,

Michael