@bompen I had this exact question and realized that nothing is written from the perspective of the taxpayer on how the numbers on the W-4P are actually used. So, I started looking for instructions written for the employers. So far, I found Publication 15-T (2024), Federal Income Tax Withholding Methods, Section 1,
Worksheet 1B. Payer’s Worksheet for Figuring Withholding From Periodic Pension or Annuity Payments https://www.irs.gov/publications/p15t#en_US_2024_publink100019110.
I'm not sure why they think we'd be happy paying no attention to the man behind the curtain!
