@dmertz Thank you for clearing that up for me. The line "Subtract the nontaxable portion of any withdrawals you took from the IRA after the rollover but before 2017." was what confused as me as I read that to mean subtract nothing (since the 401(k) money is all pretax dollars in this case) and enter full amount of rollover. Leaving the value at 0 seems to fix my basis and tax math.
The other thing I don't get is on my 1040 line 15a, the value for IRA distributions is higher than form 8606 line 16 and not sure how turbo tax came up with that number (it is higher than total for 401(k) rollover + $11k contributions + gains). I assume the "distribution" is just the conversion, but I did not convert the amount being shown on 1040 line 15a. Any ideas why that would be? I feel like I'm really fighting the TT software this year and do appreciate the time you're taking to answer my questions!
