A report inside Amazon's Ad Console (separate from the DSP new-to-brand metric) that shows ROAS/ACOS specifically for new-to-brand Sponsored Ads campaigns. New-to-brand campaigns reliably run at lower ROAS / higher ACOS than repeat-customer campaigns, since they're targeting a subset that has never bought from the brand.
Apply: Check this report to confirm the NTB gap, then use LACoS (not headline ACOS) to justify continued or increased NTB spend — a new-to-brand customer acquired at a poor headline ACOS becomes profitable once their expected repeat purchases (per Customer Lifetime Value (LTV) as the Primary Amazon Margin Lever) are counted.