I know this is an old thread, but I just came across this today. I found you can fix this by putting limitComicHeight: false, in your config
This is what mine looks like and it works great.
{
disabled: false,
module: 'MMM-CalvinAndHobbes',
position: 'middle_center',
classes: "calvin",
config: {
invertColors: false,
grayScale: false,
updateInterval: 1000 * 60 * 60 * 12,
limitComicHeight: false,
}
}
I also had to adjust my css because of the zoom, but you may not need to.
#cahcomiccontent {
zoom: 80%;
}