1. As you pointed out, the passive income is already part of your AGI. There is no subsequent addition of passive income when calculating this MAGI.
2. When calculating MAGI, the amount on Schedule 1 line 20 must be added to AGI. The amount on Schedule 1 line 20 consists only of deductible traditional IRA contributions for the year.
Worksheet 2-1 of IRS Pub 590-B details the MAGI calculation:
https://www.irs.gov/pub/irs-pdf/p590b.pdf
