Why continue to play the "guess and hope for the best" game with this? When you receive the payout, if the payor will not withhold what you request (weather they are required to by law or not, depends on the type of annuity) then once received send 30% of it to the IRS, or the percentage of difference that the payor did not withhold, and be done with this until time to file the 2019 tax return. Then if you overpaid, you'll get a refund. If you underpaid, it will definitely be under the threshold for paying any underpayment penalties.
