Just thinking broadly… one way to achieve this might be to move this “copy” logic client-side, rather than server-side, and include some toggle-able options like “Automatically copy geometry from areas” and auto-update the geofield as you select/deselect areas.
However, this is complicated… you would ALSO need to have it work server-side the same way that it does now, otherwise API-generated logs would never have their geometries populated like they do now.
Still, having some frontend options would be nice… just need to figure out how they would interact with the backend logic.