Defining the how the featured image looks in BPFun

I’m trying to define how the featured image from an article looks on the front page of BP Fun. I’ve tried editing the thumbnail but that seems to have no effect. And it just seems to grab the middle of any given picture and make that the featured article image. Is there anyway to change how the featured image gets cropped for the front page.

Sorry if this has been done a few times, I did a search and can’t find anything…

kip