Was playing with the position-visibility: anchors-visible (https://drafts.csswg.org/css-anchor-position-1/#position-visibility), and I think it might be useful to take the scrollable area's scroll-padding or the anchor's scroll-margin into consideration (https://drafts.csswg.org/css-scroll-snap/#propdef-scroll-padding). An example: https://codepen.io/kizu/pen/BaedPEB

Here we can see how if we have some fixed element reducing the effective visible area of our scrollable container, we'd want to consider it for the position-visibility. Hooking it onto scroll-margin and scroll-padding sounds logical, as this is very similar to other similar cases like scrolling or snapping to the targeted element.