Hi Kodo,
It's a bit hard to adjust the size of these image as the image is embedded directly inside the blog content itself. Hence when I'm trying to adjust one blog image on your frontpage listing, it will affect other blog images as well.
I suggest you to assign post cover as blog image instead and you can easily adjust the size of the cover by going to your backend > easyblog > settings > layout > post cover. Do not that this settings are only applicable when you set image cover as your blog image here,
http://screencast.com/t/PrgdBvzDz . After that you can set truncation options accordingly so that any embedded image inside the content will not shows up on your frontpage listing.
Hope these help.