The middle set is the 'regular scallop' set in the Large size.
To the left is the 'Petite scallops' in the Small size
The set on the right is 'Petite scallops' in the Large size.
So you can see that it's not just the scallop size that is different. The actual shape of the ovals are more squished but the other thing I love is that the actual ovals are also a lot larger so you can fit a much bigger image in them too. You can see that both 'petite scallops' sets (left & right) are bigger than the middle set! I think the petite ovals are perfect for sentiments, where I found the normal ovals too round.