That is a question to ask the IRA custodian and the account rules that they impose.
Schwab, for example, allows between 10% to 99% combined Federal and State tax to be withheld. Your financial institution might differ.
Or you can pay an estimate directly on the IRS website https://www.irs.gov/payments
Be sure to pick the right kind of payment and year.....2019 Estimate
That's true, but unless you use a 2210 form to do annualized income for a lump sum payment, or make four equal estimated payments, the withholding option avoids both since withholding is deemed to be spread through the year reguardless of when the distribution is made. As long as withholding , meets the tax burden there is no underpayment of tax penalty even if the distribution is at the end of the year.
Keep in mind that if you are under age 59½ and have no other penalty exception, the entire gross amount distributed from the IRA, including the amount withheld for taxes, will be subject to a 10% early-distribution penalty unless you come up with the money to complete a rollover of the gross amount distributed within 60 days of the distribution from the IRA. The fact that you use the money for tax withholding does not itself exempt you from this penalty. To make up for underpayment of taxes early in the year sometimes one will take an IRA distribution and have a majority of it withheld for taxes, then complete the rollover of the distribution using other funds. However, considering that you had a 401(k) loan, coming up with the money to complete the rollover might be a challenge for you.
Note that if the loan came due because you left the company, you likely did not default on the loan but the loan was instead paid off with an offset distribution. You have until the due date of your tax return for the year of the offset distribution, including extensions, to come up with the money and complete a rollover to an IRA of the amount of the offset distribution. Rolling over some or all of an offset distribution would allow continued deferral of taxes on the amount rolled over, also avoiding the early-distribution penalty on the amount rolled over.
As an aside, withholding is considered as paid evenly thru the year. So pre-paying by withholding from the IRA, late in the year, will help avoid an underpayment penalty. Making only one estimated payment (as opposed to withholding), late in the year, may result in an underpayment penalty.