Instead of using Settings > Retirement Accounts to annuitize some percentage of your IRA or 401k, you may want to set this annuity up as an Alternative Profile using a specific quote from the custodian or insurance company. 
First get a quote from an insurance company or the custodian of your IRA or 401k. Say you have a quote on an annuitization of $100,000
If you want to set that up as an Alternative Plan so that you can compare it to the Base Plan, you could do it this way:
  1. Take the amount that you want to annuitize, say the $100,000, and enter that as an IRA in the Base Plan. In other words, if you start with an IRA of $400,000 and you want to annuitize $100,000 of that amount, step one is to split that $400K account into two accounts in the Base Plan: one with $300,000 and one with $100,000. 
  2. Next create an Alternative Plan and "exclude" this new account with 100K in it (which will represent the purchase of the annuity) and then also set up the annuity in the Alt Plan with its stream of annuity payments to you based on the quote you have. 

When you compare this Alternative Plan to the Base Plan you will be evaluating the impact of annuitizing $100,000 of your $400,000 IRA.