https://www.w3.org/TR/css-backgrounds-3/#shadow-shape

For the following case:
data:text/html,<div style="width: 40px; height: 40px; border-radius: 20px; box-shadow: black 0 0 0 80px; margin: 100px">
should we expect that the outer edge of the shadow is a circle (instead of a rounded rect with the 1+(r-1)^3 adjustment)?

Perhaps we should apply the adjustment only if the radius is smaller than e.g. 1/4 of the box size?