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%; }