See existing post here: https://developer.apple.com/forums/thread/803378
When I add a UIScrollEdgeElementContainerInteraction to a view at the top of a scroll view, the blur effect doesn't always fill the full bounds of the view. The behavior changed a bit from 26.0 to 26.1 and then again in 27.0 seed 1. It depends on what subviews are there, and particularly (at least between 26.1 and 26.5) if there's a UIVisualEffectView with a glass effect.
FB20756572
The extent of the scroll edge effect was less defined on iOS 26, although the hard effect was more fixed in its extent than the soft effect.
On iOS 27 the effect is limited to the geometry presented by the sum of the UIScrollEdgeElementContainerInteractions that contribute to it. That said, the automatic, soft, and hard styles may choose to use none, some, or all of that geometry for their styling. In particular glass effects may have the least impact on overall geometry depending on how the various elements contribute.
If this sounds a bit vague, thats unfortunately because it is – the determination of the geometry can be a bit complicated at times and the intent is to produce an effect that either helps glass stand out, or make floating items (like text or images) legible, not to necessarily fill a geometric area. If your design specifically calls for filling a region, the scroll edge effect may not be what your looking for.
