Inaccuracy in iPhone touch?

Hi guys, I'm having this slight problem that I'm not sure how to fix...

In this game, I'm supposed to grab stuff and fling them. However, I tried using the Raycast method to grab the object when it detects a touch. It seems like its not that accurate though, especially for the objects further behind, due to fatfingers...

Can you guys share your methods on increasing accuracy on selecting objects on the iPhone?