Blog Images

I am implementing the Perch Blog add-on for the first time, and it is working well. The only thing I am struggling with is how to define the image size when the user uploads it. If you look here:

Test Site

The image shown in the post list is much larger than it needs to be for the layout. Where can I make this adjustment? I am familiar with Perch images but can't find where to alter this.

Thanks

Mike