On 152 ranking product pages with a detectable buy button, rendered on a phone-sized screen, the Add to Cart button starts below the first screen 82.2% of the time.
Source: PageSpeed Matters, Oct 2026. Phone render at 390x844.
Small groups; treat the gap between platforms as directional.
Source: Mobile Add to Cart Placement: 82.2% Below the Fold - PageSpeed Matters