https://api.flutter.dev/flutter/rendering/SliverGeometry/maxScrollObstructionExtent.html

says:
"Slivers that never get pinned at the edge, should return zero."

but

RenderSliverFloatingPersistentHeader sets maxScrollObstructionExtent to a non-zero value, even though RenderSliverFloatingPersistentHeader does not get pinned.