so far I understand the plugin, you need 2 files.
default 192x192 and oversized in the extended folder.
so when you have Water!400dmg.png (default 192x192) you need also
Water!400dmg.png in the extended folder of the size 400x400 to draw that one.
on my end, it does work, but I have little use for this plugin, but not sure where you got
stuck, if it persist, try to ask help there, and I'm sure they can help you if they know the
plugin or trouble on it.
as I try to help when I can and able too. [here} is the other one (opens a new tab), which might work for you.
I wish you good luck on your projects