Field curvature is much "milder" with A7 compared to A7r, top left crop:
http://www.zeissimages.com/photo.php?link=http ://www.zeissimages.com/gallery/686/U686I1397163571.SEQ.0.jpg
The branch gets to focus due to field curvature, in A7r the focus on corners would be >10m/30ft in this kind of situation.