Thanks for your reply. To answer your question, Box 2a does have an amount and the "Taxable Amount not determined" box is not checked. Your and dmertz replies, along with Turbo Tax results and a Vanguard blog I found, are all telling me the same thing (moving money from traditional 401k to roth 401k does increase MAGI, unlike a conversion from a traditional IRA to a roth IRA). I consider the issue resolved. Thanks again for your help.
