Ah, yes. Setting the arrowDxOffset to an appropriate value will resolve the issue:

showPopover(
  context: context,
  width: 120.0,
  height: 50.0,
  arrowHeight: 15.0,
  arrowWidth: 30.0,
  arrowDxOffset: -110.0, // Add this line.
  direction: PopoverDirection.top,
  bodyBuilder: (_) {
    return Center(child: const Text('Popover'));
  },
);