20% is the required federal tax withholding amount for all taxable 401K distributions. There's no way to adjust it.
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https://www.mysolo401k.net/does-the-20-federal-tax-withholding-apply-to-all-401k-distributions/
"Does the 20% Federal Tax Withholding Apply to All 401k Distributions?
No. The plan trustee should only withhold 20% for federal income tax from eligible rollover distributions.
Required Minimum Distributions
The 20% mandatory federal tax does not apply to required minimum distributions (RMDs) because RMDs are not considered eligible rollover distributions."