hi! right where the bit with the character image url is, there is a "background-size" value. it is at 200px by default, but you can make it a larger number to enlarge the image as needed. up to around 250px-300px works quite well for smaller images, it all depends.

additionally, if the character is more square than tall (something like a squirrel villager) it can also help to adjust the image itself and give it a bit of transparency at the top to help it 'stand' on the floor of the card without having to oversize it, since the code is built for centered "rectangular" images.

i hope this helps!! :}