How do I prevent a button's background image from stretching?

I'm allocating a UIButtonTypeCustom to a UIView with a background image that is smaller than the button's frame.
Reason why the image is smaller is because I'm trying to add more of a "target area" for the UIButton.
However, the image is being scaled to the full size of the frame, rather than just being the image's size.

I have tried setting the UIButton and UIButton's imageView's contentMode property to UIViewContentModeScaleAspectFit, but no luck, the image still gets stretched out.

Is there a way to do what I'm trying to do programmatically?

Thanks in advance!