RSS thumbnails too tiny / cropped?

Hi, guys. I’m co-creator of “Skin Horse” running at skin-horse.com. Site seems to be working all right but I have a question about our RSS feed (here). We run a four-panel comic but the RSS feed only broadcasts like the center two panels, and at too small a resolution to read comfortably. What would I need to tinker with in order to get the feed to display larger, complete versions of the comic? I’m comfortable with some tinkering but I am a bit of a novice at this, so please have patience and use small words. 🙂 Thanks in advance for any help!