childAnchor property
The point on the child that connects with the popover at the popover's anchor.
For example, Alignment.bottomCenter means the bottom-center point of the child will connect with the popover. See popoverAnchor for changing the popover's anchor.
Defaults to Alignment.topCenter on Android and iOS, and Alignment.bottomCenter on all other platforms.
Implementation
final AlignmentGeometry childAnchor;