To be precise, the taxable amount of the Roth conversions adds to AGI and one of the modifications to AGI for the purpose of a Roth IRA contribution is to subtract that amount back out. So if your AGI is $130,000 and $100,000 of that comes from a Roth conversion your MAGI for Roth IRA contribution purposes is $30,000, assuming no other modifications. As macuser_22 indicated, TurboTax implements this properly.
